1. in the context of speech.
(a) [16C–18C; 1990s+] a lie; a boast, an act of bragging, exaggeration; 1990s+ use may be a euph. for crap n.1 (4)
(b) [early 18C+] (orig. Irish/Scot., also craic) talk; a conversation, a chat; often constr. with the, with an added suggestion that the talk takes place within a pleasant social setting, while sense 1e refers to the setting itself [although the ety remains SE crack, recent use has incorporated Irish craic; ult. OE cracian, a crack].
(c) [late 19C+] (orig. US) a telling, sharp remark.
(d) [20C+] (orig. US) a joke.
(e) fun, amusement, informal entertainment; thus cracksome adj., jolly, amusing; also used of people.
(f) [1970s+] (US campus) a witty or funny person.
(g) [2000s] (Irish) insulting speech.
2. in the context of a sudden noise.
(a) [late 16C+] (also bum-crack, cracker) breaking wind.
(b) [mid-19C] a pistol.
(c) [mid-19C] dry wood.
(d) [late 19C–1930s] a shot from a weapon.
3. in fig. uses.
(a) [mid-17C+] any person, animal or thing that approaches perfection.
(b) [late 17C] a fop, a dandy.
(c) [18C; 1990s+] a jolly, high-spirited party.
(d) [late 18C+] the current fashion; the fashionable world, the social and sporting élite.
4. [late 17C+] a heavy blow, e.g. a crack over the head.
5. in senses of a single instance.
(a) [early 18C+] an instant, a very brief moment; usu. as in a crack
(b) [mid-19C+] an opportunity, a try, a chance.
(c) [mid-19C+] (US) a go, a time, an instance.
[late 19C+] (US) to have a try at, to get a chance to do something.
[20C+] (orig. US) to attempt, to have a try, to have a go.
[early 18C–19C] very soon, in a moment.
1. [late 19C+] to attack physically, to shoot.
2. [20C+] to make an attempt, to have a go.