larn vs catch up

larn and catch up both are verbs.

Word	Noun	Adjective	Verb	Adverb
larn	No	No	Yes	No
catch up	No	No	Yes	No

As verbs, catch up is a hyponym of larn; that is, catch up is a word with a more specific, narrower meaning than larn:

Other hyponyms of larn include relearn, absorb, assimilate, ingest, take in, hit the books, study.

larn (verb)	catch up (verb)
gain knowledge or skills	learn belatedly; find out about something after it happened
	reach the point where one should be after a delay