catch on vs cotton on

catch on and cotton on both are verbs.

Word	Noun	Adjective	Verb	Adverb
catch on	No	No	Yes	No
cotton on	No	No	Yes	No

As verbs, catch on and cotton on are synonyms defined as:

catch on and cotton on: understand, usually after some initial difficulty

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

catch on (verb)	cotton on (verb)
become popular	understand, usually after some initial difficulty
understand, usually after some initial difficulty