undulate vs fold up

undulate is an adjective but fold up is not an adjective.

Word	Noun	Adjective	Verb	Adverb
undulate	No	Yes	Yes	No
fold up	No	No	Yes	No

undulate (adjective)	fold up (adjective)
having a wavy margin and rippled surface

undulate (verb)	fold up (verb)
increase and decrease in volume or pitch, as if in waves	become folded or folded up
move in a wavy pattern or with a rising and falling motion	bend or lay so that one part covers the other
stir up (water) so as to form ripples
occur in soft rounded shapes