Old English heard "solid, firm, not soft," also "severe, rigorous, cruel," from Proto-Germanic *hardu- (cf. Old Saxon and Dutch hard, Old Norse harðr "hard," Old High German harto "extremely, very," German hart, Gothic hardus "hard"), from PIE *kortu-, (cf. Greek kratos "strength," kratys "strong"), from root *kar-/*ker- "hard." Meaning "difficult to do" is from c.1200. The adverb sense was also present in Old English.
Hard of hearing preserves obsolete Middle English sense of "having difficulty in doing something." Hard liquor is 1879, American English (hard drink is from 1810; hard cider is from 1789), and this probably led to hard drugs (1955). Hard facts is from 1887; hard news is from 1938. Hard copy (as opposed to computer record) is from 1964; hard disk is from 1978. Hard up (1610s) is originally nautical, of steering (slang sense of "short of money" is from 1821), as is hard and fast (1680s), of a ship on shore. Hard times "period of poverty" is from 1705.
Hard money (1706) is specie, as opposed to paper. Hence 19c. U.S. hard (n.) "one who advocates the use of metallic money as the national currency" (1844). To play hard to get is from 1945. Hard rock as a pop music style recorded from 1967.