Cerberus (various): The triple-headed dog who guards Tartarus, the Greek version of Purgatory.
Chac (FFX2): Chac is the Mayan god of rain and thunder.
Chimera (various): From Greek mythology. It's a fire-breathing monster having either the hindquarters of a serpent and the head of a lion on the body of a goat, or else the back of a goat, the wings of a dragon, the front half of a lion, and three heads (one each for goat, lion and dragon). In Square games they favor the latter description, adding in a snake for a tail.
Chimerageist (FF10): "Geist" is German for "spirit", so the name means "Chimera Spirit".
Claret Dragon (FFX2): Claret is a dark, purplish red color, which matches the color of the dragon's body.
Cockatrice (various): Supposedly they were deadly winged serpents from biblical times. It is said in a legend that, when the moons are just right, a chicken somewhere will lay an egg. On that night, a snake will appear and curl itself around that egg. When the egg hatches, a fearful monster called a "cockatrice" emerges from it. The monster, half bird and half snake; has the powers of the Gorgon, and can turn people into stone just by people looking at them.
Coeurl (various): The "cuarl" is almost surely based on the "coeurl" from A.E. Van Voght's short story "Black Destroyer". In it, there's an alien creature resembling a panther with tentacles and psionic powers. The Displacer Beast (from Dungeons and Dragons) was also likely based on this monster. There's also a monster called Coeurlregina in FF10, which basically means "Coeurl Queen", "regina" being Latin for "queen".
Daeva (FFX2): A group of demons in the middle east, yet gods in the far-east, especially Hinduism.
Dark Side (FF6): Maybe this has something to do with "the Force" in the Star Wars movies; Darth Vader is on the Dark Side. Probably just coincidence, though.
Demonolith (FF10): Demon + Monolith.
Dingo (FF10): The name of a canine animal indigenous to Australia.
Dream Stooges (FF6): In Japan, their names were Sueño, Sogno, and Rêve. The names mean "dream" in Spanish, Italian, and French, respectively.
Dullahan (FF2, FF6, FFMQ): Dullahan is from Irish mythology, and is a headless spirit that wanders around Ireland, holding his head under his arm and driving a black coach drawn by headless horses! He knocks on people's doors, and hurls a bucket of blood in their faces! A visit from Dullahan is considered to be a portent of death.
Eland (FF6): Shows up not only on the Veldt in FF6, but on the "real" veldt in Africa. It's a big antelope with horns.
Epitaph (FF9): This tombstone-like monster appropriately obtains its name from the general word for inscriptions upon a gravestone.
Espada (FF10): Spanish for "sword".
Fafnir (FF10): The dragon killed by Siegfried in the Ring of the Nibelung Norse legend. See Siegfried for more info. Fafnir also appears in the Japanese version of FF6 (it was translated as Vectaur).
Farfarello (FF5): Shows up in the forest part of the Cleft of Dimension, is another demon from Dante's Inferno. Some of the others
are the Four Fiends in FF2. This monster was translated as "Jestrex" for some reason in the PSX version.
Fastitocalon (FF8): In Tolkien's Middle Earth series, the Fastitocalon were huge turtle-fish monsters in Hobbit lore that were often mistaken for islands.
Fenrir (FF10): See Summons.
Figaliz (FF6): Short for "Figaro Lizard".
Flan (various): This is a type of dessert. Also note the "puddings" and "mousse"s that have variations on this. The monster in FF6 called Muus is in fact supposed to be "mousse". FFX2's Flans each have Spanish names: Amarillo = Yellow, Azabache = Jet Black, Azul (Azule) = Blue, Palido = white wine-grape; pale, Rojo = Red
Fortis (FF6): Comes from Latin and means strength or power.
Frost Giants (FF1): The Frost Giants come from Nordic mythology. The father of the Frost Giants was Ymir, and with his cow Audumla he created the Aesir, and Odin is among them.
Fury (FF5): The Furies were old crones sent by the gods to punish people. Supposedly, they carried whips with thorns on them.
Gandarewa (FF10): Gandarew is a Persian water demon that attempts to devour the good things of creation.
Gargoyles (FF5): Stone statues that are frequently seen near entrances to buildings. They guard the entrances to the places where the slabs are located. Some old European castles would have gargoyles above the door to ward off evil spirits. Goyles and Red Goyles are in FF1 also.
Garm (FF6): In Nordic myths, Garm is a dog who is killed by Tyr at Ragnarok.
Garuda (FF10): The bird that Vishnu rode on in Hindu legend. Garuda is the king of all birds in Hindu mythology and supposedly can carry several gods without impediment. Garuda represents good, and can sense evil in its vicinity.
Gemini (FF10): The Twins of Zodiac fame. The two Iron Giant-type monsters always appear together, hence the name.
Gerogero (FF8): This is a Japanese onomatapoeia word for 'throwing up'.
Gilgame (FF5): 'Gil' is the basic currency of the FF series and 'game' is turtle (ishigame to be more correct, ishigame is various turtles and kame is tortoise or turtle).
Gnoll (FF9): From Dungeons and Dragons, the gnoll is described as a tall desert-dwelling humanoid with the head of a hyena & greyish green fur.
Gnoma Entite (FF12): "Gnoma" comes from "gnome". The gnomes were small dwarf-like creatures who lived in the earth, and were sometimes regarded as being earth spirits.
Grasharaboras (FF6): Known as Borras in the American version. See Summons.
Grendel (FF8, FF10): A monster fought by the legendary Beowulf. See Characters for more info on Beowulf.
Grosspanzer (FF7): This is German for "Grand Armor".
Gucumatz (FFX2): There is a Mayan epic known as the Popol Vuh that contains the tale of a hero named Gucumatz who possesses the ability to trnasform into a variety of animals.
Gug (FFX2): Likely derived of Gog, a giant who with his partner Magog appear in Revelations to symbolize the future enemies of God. Gug is an ogre-like monster from H.P Lovecraft's Cthulu mythos with a giant gaping maw for a head. Minus the maw-for-a-head, FFX-2's Gug fits a similar description.
Halicarnassus (FF5): One of the bosses of the Cleft of Dimension. The name probably comes from the Mausoleum at Halicarnassus, which was
built in what is now Turkey around 350 BC. It was built for Carian king Mausolus; thus the English word "mausoleum". Incidentally, this is another Wonder of the Ancient World. This name was also butchered in the PSX translation as "Halycanos".
Halma (FF10): Greek for "jump".
Haokah (FF3): According to Encyclopedia Mythica, he's the Sioux god of thunder, and sometimes the god of the hunt. That fits given he uses a thunder attack.
Hecteyes (FF2, FF9): English for "hundred eyes".
Hilgigars (FF9): Should be "Hill Gigas".
Hipocampus (FF6): In Greek mythology, a hippocampus was a sea creature that resembled a horse with the lower body of a dolphin or fish. One of these was what pulled Poseidon's chariot.
Hrimthurs (FFX2): Hrimthurs was a god in Norse mythology that constructed the walls surrounding Asgard.
Humpty (FF6): Probably comes from the poem, "Humpty Dumpty".
Hydra (FF4): See Hydra.
Ibises (FF5): An ibis is a type of bird much represented in Egyptian mythology. In the PSX version, though, there were translated as "Avis"es, from the Latin for "to fly". "Tote Avis" could either mean "Death Ibis" ('Tod' (rhymes with boat) is German for 'death') or "Thoth Ibis" (as in the Egyptian god who kept balance in the world, and who had the head of an ibis). Also "Jura Avis/Ibis" may be related to the Jurassic period in history, which is in turn named for the Jura mountains in Switzerland. "Avis" is probably the correct translation, I believe.
Intangir (FF6): Probably from 'intangible'... he's pretty hard to hit! Maou mentions that Intangir was "Nemureru Shishi," "Sleeping Lion," in the Japanese version.
Io (FF6): The name of Jupiter's volcanic moon. Jupiter's four lovers included Io, Europa, Callisto, and Ganymede - they're immortalized as Jupiter's four largest moons. It should be pronounced "EE-oh", but you also hear "EYE-oh". The Columbia Encyclopedia entry for Io: "In Greek mythology, daughter of Inachus, king of Argos. She was loved by Zeus, who, to protect her from Hera's jealousy, changed her into a white heifer. Hera, however, was not deceived; she claimed the heifer and sent Argus to guard it. When Hermes killed Argus, Hera tormented Io with a gadfly which drove her across Europe and through Asia, until she was finally allowed to rest in Egypt. There Zeus returned her to human form, and she bore his child Epaphus. Io has been identified with the Egyptian goddess Isis."
Ironside (FFX2): This may refer to the warship U.S.S. Constitution. In the 1800s, it was referred to as "Old Ironsides". Ironside was a regiment led by Oliver Cromwell during the English Civil War (early 1600s) against King James I.
Jabberwock (FF9): The Jabberwock comes from Lewis Carroll's poem 'Jabberwocky", quoted in "Alice Through The Looking-Glass".
Jahi (FFX2): Jahi is a Persian demoness of debauchery.
Jormungard: See Terrato / Midgard Serpent.
Jubjub (FF11): The Jubjub Bird comes from Lewis Carroll's poem 'Jabberwocky", quoted in "Alice Through The Looking-Glass".
Kary (FF1, FF9): The Fiend of Fire in FF1, Kary could be an alternate spelling of Kali from Indian myths. Kali demanded human sacrifices of her worshipers and had skin blacker than the night sky. She had three eyes, four arms, and giant tusks coming from her mouth. The boss character Kary itself is based on a Hindu goddess. Kali was the three-eyed female counterpart of Shiva the Destroyer in Hindu mythology. When they danced, they wrought destruction upon the world, though they each had the power to keep the other in check and help maintain balance in the universe. Kary was also called Marilith in the JP version, so likely only the name has this origin, the creature was not based on the myth.
Kelpie
(FF3): A water spirit in Scottish folklore that appears as horse and leads children and weary travelers into water in order to drown them.