crack (v.)
Old English cracian "make a sharp noise," from Proto-Germanic *krakojan (cognates: Middle Dutch craken, Dutch kraken, German krachen), probably imitative. Related: Cracked; cracking. To crack a smile is from 1840s; to crack the whip in the figurative sense is from 1940s.
crack (n.)
"split, opening," 14c., from crack (v.). Meaning "try, attempt" first attested 1836, probably a hunting metaphor, from slang sense of "fire a gun." Meaning "rock cocaine" is first attested 1985. The superstition that it is bad luck to step on sidewalk cracks has been traced to c.1890. Adjectival meaning "top-notch, superior" (as in a crack shot) is slang from 1793.