catchword vs locution

catchword and locution both are nouns.

Word	Noun	Adjective	Verb	Adverb
catchword	Yes	No	No	No
locution	Yes	No	No	No

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

catchword: a favorite saying of a group, organization or individual
locution: a word or phrase that particular people use in particular situations

Other hypernyms of catchword include expression, saying.

catchword (noun)	locution (noun)
a favorite saying of a group, organization or individual	a word or phrase that particular people use in particular situations
a word printed at the top of the page of a dictionary or other reference book to indicate the first or last item on that page