From Greek 'gígas' — likely borrowed from a pre-Greek Mediterranean language along with much of Greek mythology.
An imaginary or mythical being of human form but superhuman size; a person or thing of unusual size or power.
From Old French 'geant' (Modern French 'géant'), from Latin 'gigās' (genitive 'gigantis'), from Greek 'gígas' (γίγας, one of the Giants who warred against the Olympian gods). The ultimate origin is pre-Greek — the word has no convincing Indo-European etymology and likely comes from a pre-Greek Mediterranean substrate language, the same source that produced many Greek mythological names. The Giants (Gigantes) were born from Gaia (Earth) and the blood
The word 'giant' is probably older than Greek itself. 'Gígas' has no convincing Indo-European etymology and likely comes from a pre-Greek language spoken in the Aegean before the Greeks arrived (c. 2000 BCE). Many Greek mythological terms — Olympus, labyrinth, Athena, Hermes — similarly have pre-Greek origins, suggesting that the arriving Greeks absorbed an older civilization's mythology wholesale and kept the original names.