tongue twister vs locution

tongue twister and locution both are nouns.

Word	Noun	Adjective	Verb	Adverb
tongue twister	Yes	No	No	No
locution	Yes	No	No	No

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

tongue twister: an expression that is difficult to articulate clearly
locution: a word or phrase that particular people use in particular situations

Other hypernyms of tongue twister include expression, saying.

tongue twister (noun)	locution (noun)
an expression that is difficult to articulate clearly	a word or phrase that particular people use in particular situations