headband n.

Old English heafod "top of the body," also "upper end of a slope," also "chief person, leader, ruler; capital city," from Proto-Germanic *haubid (source also of Old Saxon hobid, Old Norse hofuð, Old Frisian haved, Middle Dutch hovet, Dutch hoofd, Old High German houbit, German Haupt, Gothic haubiþ "head"), from PIE root *kaput- "head."

Modern spelling is early 15c., representing what was then a long vowel (as in heat) and remained after pronunciation shifted. Of rounded tops of plants from late 14c. Meaning "origin of a river" is mid-14c. Meaning "obverse of a coin" (the side with the portrait) is from 1680s; meaning "foam on a mug of beer" is first attested 1540s; meaning "toilet" is from 1748, based on location of crew toilet in the bow (or head) of a ship.

Synechdochic use for "person" (as in head count) is first attested late 13c.; of cattle, etc., in this sense from 1510s. As a height measure of persons, from c. 1300. Meaning "drug addict" (usually in a compound with the preferred drug as the first element) is from 1911.

To be over (one's) head "beyond one's comprehension" is by 1620s. To give head "perform fellatio" is from 1950s. Phrase heads will roll "people will be punished" (1930) translates Adolf Hitler. Head case "eccentric or insane person" is from 1966. Head game "mental manipulation" attested by 1972.

"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."