get it vs cotton on

get it and cotton on both are verbs.

Word	Noun	Adjective	Verb	Adverb
get it	No	No	Yes	No
cotton on	No	No	Yes	No

As verbs, get it and cotton on are synonyms defined as:

Other synonyms of get it include catch on, get onto, get wise, latch on, tumble, twig.

get it (verb)	cotton on (verb)
understand, usually after some initial difficulty	understand, usually after some initial difficulty
receive punishment; be scolded or reprimanded