Is it ensure, insure, or assure?
late Old English hyttan, hittan "come upon, meet with, fall in with, 'hit' upon," from a Scandinavian source, cf. Old Norse hitta "to light upon, meet with," also "to hit, strike;" Swedish hitta "to find," Danish and Norwegian hitte "to hit, find," from Proto-Germanic *hitjanan. Related: Hitting. Meaning shifted in late Old English period to "strike," via "to reach with a blow or missile," and replaced Old English slean in this sense. Original sense survives in phrases such as hit it off (1780, earlier in same sense hit it, 1630s) and is revived in hit on (1970s).
Underworld slang meaning "to kill by plan" is 1955 (as a noun in this sense from 1970). To hit the bottle "drink alcohol" is from 1889. To hit the nail on the head (1570s) is from archery. Hit the road "leave" is from 1873; to hit (someone) up "request something" is from 1917. Hit and run is 1899 as a baseball play, 1924 as a driver failing to stop at a crash he caused. To not know what hit (one) is from 1923.
late 15c., "a rebuke;" 1590s as "a blow," from hit (v.). Meaning "successful play, song, person," etc., 1811, is from the verbal sense of "to hit the mark, succeed" (c.1400). Underworld slang meaning "a killing" is from 1970. Meaning "dose of narcotic" is 1951, from phrases such as hit the bottle.
To inject a narcotic; shoot up
[1940s+ Narcotics; an earlier related sense, ''to drink to excess,'' found by 1900]
: a hit musical/ a hit songnoun