arrow-head (n.)

"slender, pointed missile weapon, made to be shot from a bow," early 14c., from Old English arwan, earlier earh "arrow," possibly borrowed from Old Norse ör (genitive örvar), from Proto-Germanic *arkhwo (source also of Gothic arhwanza), from PIE root *arku-, source of Latin arcus (see arc (n.)). The etymological sense would be "the thing belonging to the bow." The meaning "a mark like an arrow" in cartography, etc. is from 1834.

It was a rare word in Old English. More common words for "arrow" were stræl (which is cognate with the word still common in Slavic and once prevalent in Germanic, related to words meaning "flash, streak") and fla, flan (the -n perhaps mistaken for a plural inflection), from Old Norse, a North Germanic word, perhaps originally with the sense of "splinter." Stræl disappeared by 1200; fla became flo in early Middle English and lingered in Scottish until after 1500.

Robyn bent his joly bowe,

Therein he set a flo.

["Robyn and Gandelyn," in a minstrel book from c. 1450 in the British Museum]

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.