suck in vs suck

suck in is not a noun while suck is a noun.

Word	Noun	Adjective	Verb	Adverb
suck in	No	No	Yes	No
suck	Yes	No	Yes	No

As verbs, suck in and suck are synonyms defined as:

suck in and suck: attract by using an inexorable force, inducement, etc.

suck in (noun)	suck (noun)
	the act of sucking

suck in (verb)	suck (verb)
take up as if with a sponge	give suck to
draw in as if by suction	draw into the mouth by creating a practical vacuum in the mouth
attract by using an inexorable force, inducement, etc.	take in, also metaphorically
	draw something in by or as if by a vacuum
	provide sexual gratification through oral stimulation
	be inadequate or objectionable
	attract by using an inexorable force, inducement, etc.