crunch (v.)

1814, "crush with the teeth," a variant of craunch (1630s), which probably is of imitative origin. Meaning "act or proceed with a sound of crunching" is by 1849. Related: Crunched; crunching.

The noun is 1836, "an act of crunching," from the verb; the sense of "critical moment" was popularized 1939 by Winston Churchill, who had used it in his 1938 biography of Marlborough.

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Definitions of crunch from WordNet
crunch (v.)
make a crushing noise;
his shoes were crunching on the gravel
Synonyms: scranch / scraunch / crackle
crunch (v.)
press or grind with a crushing noise;
Synonyms: cranch / craunch / grind
crunch (v.)
chew noisily;
The children crunched the celery sticks
Synonyms: munch
crunch (v.)
reduce to small pieces or particles by pounding or abrading;
Synonyms: grind / mash / bray / comminute
crunch (n.)
the sound of something crunching;
he heard the crunch of footsteps on the gravel path
crunch (n.)
a critical situation that arises because of a shortage (as a shortage of time or money or resources);
a financial crunch
an end-of-the year crunch
crunch (n.)
the act of crushing;
Synonyms: crush / compaction