good-for-naught vs meritless

good-for-naught is a noun but meritless is not a noun.

Word	Noun	Adjective	Verb	Adverb
good-for-naught	Yes	Yes	No	No
meritless	No	Yes	No	No

As adjectives, good-for-naught and meritless are synonyms defined as:

good-for-naught and meritless: without merit; of little or no value or use

Other synonyms of good-for-naught include good-for-nothing, no-account, no-count, no-good, sorry.

good-for-naught (noun)	meritless (noun)
an idle worthless person

good-for-naught (adjective)	meritless (adjective)
without merit; of little or no value or use	without merit; of little or no value or use