flex vs curl

flex and curl both are nouns.

Word	Noun	Adjective	Verb	Adverb
flex	Yes	No	Yes	No
curl	Yes	No	Yes	No

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

flex (noun)	curl (noun)
the act of flexing	lock of hair in the shape of a spiral or curl
	a round shape formed by a series of concentric circles (as formed by leaves or flower petals)

flex (verb)	curl (verb)
cause (an object) to assume a crooked or angular form	form a curl, curve, or kink
bend a joint	play the Scottish game of curling
form a curve	twist or roll into coils or ringlets
contract	wind around something in coils or loops
exhibit the strength of	shape one's body into a curl