#1 crack v. [check, break] become fractured; break or crack on the surface only; "The glass cracked when it was heated". wn
#2 crack v. make a very sharp explosive sound; "His gun cracked". wn
#3 crack n. [cleft, crevice, fissure, scissure] a long narrow opening. wn
#4 crack s. [ace, A-one, first-rate, super, tiptop, topnotch, top-notch, tops] of the highest quality; "an ace reporter"; "a crack shot"; "a first-rate golfer"; "a super party"; "played top-notch tennis"; "an athlete in tiptop condition"; "she is absolutely tops". wn
#5 crack n. [gap] a narrow opening; "he opened the window a crack". wn
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