good-for-naught

The noun has one meaning:

Meaning #1: an idle worthless person
  Synonyms: goldbrick, goof-off, ne'er-do-well, good-for-nothing

The adjective good-for-naught has one meaning:

Meaning #1: without merit
  Synonyms: good-for-nothing, meritless, no-account, no-count, no-good, sorry