"assent," 1570s, of unknown origin, perhaps a variant of I, meaning "I assent;" or an alteration of Middle English yai "yes" (see yea), or from aye, adv. "always, ever."

"always, ever," c.1200, from Old Norse ei "ever" (cognate with Old English a "always, ever"), from PIE *aiw- "vital force, life, long life, eternity" (cognates: Greek aion "age, eternity," Latin aevum "space of time;" see eon).