slang vs bunk off

slang is a noun but bunk off is not a noun.

Word	Noun	Adjective	Verb	Adverb
slang	Yes	No	Yes	No
bunk off	No	No	Yes	No

slang (noun)	bunk off (noun)
a characteristic language of a particular group (as among thieves)
informal language consisting of words and expressions that are not considered appropriate for formal occasions; often vituperative or vulgar

slang (verb)	bunk off (verb)
abuse with coarse language	play truant from work or school
fool or hoax
use slang or vulgar language