Q From Jim True: Is there any connection between the two adjectives, giant and gigantic? It seems to me there must be, and if so, where did the extra g in the latter come from?
A A connection does exist: they both derive from the same word of the classical Greek period. The difference in spelling came about because their journeys into English took separate paths.
The Greek word was gigas, in compounds as gigant-. (The modern number prefix giga- for a thousand million was based on the Greek root.) The Romans borrowed both to make the Latin noun gigas and its adjective gigantem. Old English took its word for giant from the Latin adjective, making gigant. This survived in the language for several centuries, though it is long since defunct.
That’s because of the Norman Conquest, following which English was influenced heavily by Norman French. By the 1290s, English people had taken over the Old French word for a giant. This did similarly derive from Latin, but had been greatly modified along the way and was said and spelled differently, as géant, jéant or gaiant. English adopted the geant version.
Around 1600, writers created two new adjectives, gigantean and gigantic. The source is unclear (Robert Barnhart commented rather sadly in the gigantic entry in his Dictionary of Etymology that “a long literary history of reference ... makes determination of the word’s immediate source difficult to establish”). It could have been from the Latin adjective gigantem, or perhaps from the Greek gigant-, or even possibly with a nod to the Old English gigant, which was still around, though overshadowed by the geant version.
However it happened, the adjective settled down to be gigantic. In turn, its influence shifted geant to giant.
By the way, gargantuan, for a giant with a prodigious appetite, has an independent origin. The source is stories by the sixteenth-century French writer François Rabelais about the giant Gargantua. It’s not obvious where Rabelais got the name: a French etymological work argues a connection with gorge, throat, and gargariser, to gargle.