Band-Aid n.

"a flat strip," also "something that binds," Middle English bende, from Old English bend "bond, fetter, shackle, chain, that by which someone or something is bound; ribbon, ornament, chaplet, crown," with later senses and spelling from cognate Old Norse band and technical senses from Old French bande "strip, edge, side" (12c., Old North French bende), all three ultimately from Proto-Germanic *bindan, from PIE root *bhendh- "to bind."

The meaning "a flat strip" (late 14c.) is from French. In Middle English, this was sometimes distinguished by the spelling bande, bonde, but with loss of terminal -e the words have fully merged via the notion of "flat strip of flexible material used to wind around something."

The meaning "broad stripe of color, ray of colored light" is from late 14c.; the electronics sense of "range of frequencies or wavelengths" is from 1922. Most of the figurative senses ("legal or moral commitment; captivity, imprisonment," etc.) have passed into bond (n.), which originally was a phonetic variant of this band. The Middle English form of the word is retained in heraldic bend (n.2) "broad diagonal stripe on a coat-of-arms."

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.