click (v.)youdaoicibaDictYouDict[click 词源字典]
1580s, of imitative origin (compare Dutch and East Frisian klikken "to click; Old French clique "tick of a clock"). The figurative sense, in reference usually to persons, "hit it off at once, become friendly upon meeting" is from 1915, perhaps based on the sound of a key in a lock. Related: Clicked; clicking.[click etymology, click origin, 英语词源]
hit (v.)youdaoicibaDictYouDict
late Old English hyttan, hittan "come upon, meet with, fall in with, 'hit' upon," from a Scandinavian source such as 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 *hitjan, of uncertain origin. 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.