The story
From Ancient Greek ἑκᾰτόν (hekătón, “hundred”) + χείρ (kheír, “hand”), compare the adjective ἑκατόγχειρος (hekatónkheiros, “hundred-handed”). The putative *Ἑκατόγχειρες (*Hekatónkheires) is unattested in Hesiod's Theogony, which instead describes the giants with the phrase ἑκατὸν μὲν χεῖρες (hekatòn mèn kheîres).
Etymology from Wiktionary, CC BY-SA 4.0.