Source : Webster's Revised Unabridged Dictionary (1913)

Libelous \Li"bel*ous\ (l[imac]"b[e^]l*[u^]s), a.
   Containing or involving a libel; defamatory; containing that
   which exposes some person to public hatred, contempt, or
   ridicule; as, a libelous pamphlet. [Written also
   {libellous}.] -- {Li"bel*ous*ly}, adv.

Source : WordNet®

libelous
     adj : (used of statements) harmful and often untrue; tending to
           discredit or malign [syn: {calumniatory}, {calumnious},
            {defamatory}, {denigrative}, {denigrating}, {denigratory},
            {libellous}, {slanderous}]