flex vs draw in

flex is a noun but draw in is not a noun.

Word	Noun	Adjective	Verb	Adverb
flex	Yes	No	Yes	No
draw in	No	No	Yes	No

As verbs, draw in is a hyponym of flex; that is, draw in is a word with a more specific, narrower meaning than flex:

flex (noun)	draw in (noun)
the act of flexing

flex (verb)	draw in (verb)
cause (an object) to assume a crooked or angular form	direct toward itself or oneself by means of some psychological power or physical attributes
bend a joint	draw in as if by suction
form a curve	pull inward or towards a center
contract	of trains; move into (a station)
exhibit the strength of	advance or converge on
	shape one's body into a curl