WordWeb Online

1. Lacking in usefulness or value
   "a worthless idler"
    
2. Morally reprehensible
   - despicable, ugly, vile, slimy, unworthy, wretched

See also: chaffy, evil, good-for-naught, good-for-nothing, manky [Brit], meritless, negligible, no-account, no-count, no-good, nugatory, otiose, paltry, pointless, purposeless, rubbishy, schlocky, senseless, sorry, superfluous, tinpot [Brit], trashy, trifling, unworthy, valueless, wasted

Antonym: valuable