scrunch up vs ruck

scrunch up is not a noun while ruck is a noun.

Word	Noun	Adjective	Verb	Adverb
scrunch up	No	No	Yes	No
ruck	Yes	No	Yes	No

As verbs, ruck is a hyponym of scrunch up; that is, ruck is a word with a more specific, narrower meaning than scrunch up:

scrunch up: make wrinkles or creases on a smooth surface; make a pressed, folded or wrinkled line in; `crisp' is archaic
ruck: become wrinkled or drawn together

Other hyponyms of scrunch up include cockle, crumple, knit, pucker, rumple, pucker, ruck up.

scrunch up (noun)	ruck (noun)
	a crowd especially of ordinary or undistinguished persons or things
	an irregular fold in an otherwise even surface (as in cloth)

scrunch up (verb)	ruck (verb)
make wrinkles or creases on a smooth surface; make a pressed, folded or wrinkled line in; `crisp' is archaic	become wrinkled or drawn together
sit on one's heels