A crack in the sidewalk.
A crack shot (expert marksman).
A crack of a whip.
A “crack” about someone’s lack of intelligence.
A “crack baby.”

The crack of dawn; to crack a smile, crack a joke, crack an egg, a nut, crack a book.

Cracking up (bursting out in laughter or going insane). He is “half-cracked.”

The meaning of the word “crack” would appear to be entirely dependent on its context. The core meaning, however, is rooted in phonetic materiality; the word is an onomatopeia for the sound of something brittle being fractured. By metaphorical extension, the result of such a fracture; a fissure or gap, a fractured composure or sanity; an aggressive remark, etc... It could not be used, except ironically, for something smooth, unfractured, soft-sounding.