slang word vs locution

slang word and locution both are nouns.

Word	Noun	Adjective	Verb	Adverb
slang word	Yes	No	No	No
locution	Yes	No	No	No

As nouns, locution is a hypernym of slang word; that is, locution is a word with a broader meaning than slang word:

slang word: a word or expression that is outside of standard usage and is very informal
locution: a word or phrase that particular people use in particular situations

Other hypernyms of slang word include expression, saying.

slang word (noun)	locution (noun)
a word or expression that is outside of standard usage and is very informal	a word or phrase that particular people use in particular situations