suck up vs kowtow

suck up is not a noun while kowtow is a noun.

Word	Noun	Adjective	Verb	Adverb
suck up	No	No	Yes	No
kowtow	Yes	No	Yes	No

As verbs, suck up and kowtow are synonyms defined as:

Other synonyms of suck up include bootlick, fawn, kotow, toady, truckle.

suck up (noun)	kowtow (noun)
	a former Chinese custom of touching the ground with the forehead as a sign of respect or submission

suck up (verb)	kowtow (verb)
try to gain favor by cringing or flattering	try to gain favor by cringing or flattering
take in, also metaphorically	bend the knees and bow in a servile manner
ingratiate oneself to; often with insincere behavior