frolic vs lark about

frolic is a noun but lark about is not a noun.

Word	Noun	Adjective	Verb	Adverb
frolic	Yes	No	Yes	No
lark about	No	No	Yes	No

As verbs, frolic and lark about are synonyms defined as:

Other synonyms of frolic include cavort, disport, frisk, gambol, lark, rollick, romp, run around, skylark, sport.

frolic (noun)	lark about (noun)
gay or light-hearted recreational activity for diversion or amusement

frolic (verb)	lark about (verb)
play boisterously	play boisterously