no-account vs meritless

no-account is a noun but meritless is not a noun.

Word	Noun	Adjective	Verb	Adverb
no-account	Yes	Yes	No	No
meritless	No	Yes	No	No

As adjectives, no-account and meritless are synonyms defined as:

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

no-account (noun)	meritless (noun)
an idle worthless person

no-account (adjective)	meritless (adjective)
without merit; of little or no value or use	without merit; of little or no value or use