undulate vs ripple

undulate is not a noun while ripple is a noun.

Word	Noun	Adjective	Verb	Adverb
undulate	No	Yes	Yes	No
ripple	Yes	No	Yes	No

As verbs, undulate and ripple are synonyms defined as:

Other synonyms of undulate include cockle, riffle, ruffle.

undulate (noun)	ripple (noun)
	a small wave on the surface of a liquid
	(electronics) an oscillation of small amplitude imposed on top of a steady value

undulate (adjective)	ripple (adjective)
having a wavy margin and rippled surface

undulate (verb)	ripple (verb)
increase and decrease in volume or pitch, as if in waves	stir up (water) so as to form ripples
move in a wavy pattern or with a rising and falling motion	flow in an irregular current with a bubbling noise
stir up (water) so as to form ripples
occur in soft rounded shapes