"assent," 1576, perhaps a variant of I, meaning "I assent," or an alt. of M.E. yai "yes."
aye (2)
"always, ever," c.1200, from O.N. ei "ever" (cognate with O.E. a "always, ever"), from PIE *aiw- "vital force, life, long life, eternity" (cf. Gk. aion "age, eternity," L. aevum "space of time;" see eon).