sit down vs scrunch

sit down is not a noun while scrunch is a noun.

Word	Noun	Adjective	Verb	Adverb
sit down	No	No	Yes	No
scrunch	Yes	No	Yes	No

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

sit down: be in a position in which one's upper body is largely upright and supported by one's backside
scrunch: sit on one's heels

Other hyponyms of sit down include lounge, sprawl, perch, rest, roost, crouch, hunker, hunker down, scrunch up, squat.

sit down (noun)	scrunch (noun)
	a crunching noise

sit down (verb)	scrunch (verb)
show to a seat; assign a seat for	make wrinkles or creases on a smooth surface; make a pressed, folded or wrinkled line in; `crisp' is archaic
be in a position in which one's upper body is largely upright and supported by one's backside	sit on one's heels
take a seat	make a noise typical of an engine lacking lubricants