early 15c., aide, "war-time tax," also "help, support, assistance," from Old French aide, earlier aiudha "aid, help, assistance," from Late Latin adiuta, noun use of fem. of adiutus, past participle of Latin adiuvare "to give help to," from ad "to" (see ad-) + iuvare "to help, give strength, support, sustain," which is from a PIE source perhaps related to the root of iuvenis "young person" (see young (adj.)).
The meaning "thing by which assistance is given" is recorded from 1590s; the sense of "person who assists, helper" is from 1560s. The meaning "material help given by one country to another" is from 1940.