chin up vs chin

chin up is not a noun while chin is a noun.

Word	Noun	Adjective	Verb	Adverb
chin up	No	No	Yes	No
chin	Yes	No	Yes	No

As verbs, chin up and chin are synonyms defined as:

chin up and chin: raise oneself while hanging from one's hands until one's chin is level with the support bar

chin up (noun)	chin (noun)
	the protruding part of the lower jaw

chin up (verb)	chin (verb)
raise oneself while hanging from one's hands until one's chin is level with the support bar	raise oneself while hanging from one's hands until one's chin is level with the support bar