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.
1892, from crunch (n.) + -y (2). Student slang sense of "annoyingly intense about health or environmental issues" is by 1990, short for crunchy granola (considered a natural and wholesome food) used as an adjective. It could be neutral or positive at first, but later often was dismissive. Related: Crunchiness.
"chew deliberately or continuously," early 15c. variant of mocchen (late 14c.), imitative (with -n- perhaps by influence of crunch), or perhaps from or influenced by Old French mangier "to eat, bite," from Latin manducare "to chew." Related: Munched; munching.
1825, "to bite, crush with or as with the teeth," intensive form of crunch (v.); ultimately imitative (see scr-). The colloquial meaning "to squeeze, crush" is by 1835 (implied in scrunched). The intransitive sense of "contract oneself into a more compact shape" is by 1884. Related: Scrunching. As a noun, "noise made by scrunching," by 1857; as an adjective, scrunchy is attested by 1905.
"mass of finely minced and seasoned meat or fish made into small balls and fried," 1706, from French croquette (17c.), from croquer "to crunch" (imitative) + diminutive suffix -ette.
1520s, "to chew noisily, crunch;" 1570s (of horses) "to bite repeatedly and impatiently," probably echoic; OED suggests a connection with jam (v.). Earlier also cham, chamb, etc. (late 14c.). To champ on (or at) the bit, as an eager horse will, is attested in the figurative sense by 1640s. Related: Champed; champing. As a noun, "act of biting repeatedly, action of champing," from c. 1600.
initial sound-cluster, containing the exceptions to the general rule that sc- or sk- in Modern English indicates a word not from Old English (whose sc- regularly becomes sh-). Words often are found in pairs, especially in dialect and slang, one in scr-, one in shr- (or schr-); a prominent surviving example is shred and screed, the same Old English word surviving in two forms now much different in meaning.
OED also notes that "Many English words beginning with scr- agree more or less closely in meaning with other words differing from them in form only by the absence of the initial s" (such as crunch/scrunch, scringe, an alternative form of cringe, etc.)
It does not appear that these coincidences are due to any one general cause ..., but it is probable that the existence of many pairs of synonyms with scr- and cr- produced a tendency to change cr-, in words expressive of sounds or physical movements, into scr- so as to render the word echoic or phonetically symbolic. [OED]