The Collaborative International Dictionary of English v.0.48:

Felonious \Fe*lo"ni*ous\, a.
   Having the quality of felony; malignant; malicious;
   villainous; traitorous; perfidious; in a legal sense, done
   with intent to commit a crime; as, felonious homicide.
   [1913 Webster]

         O thievish Night,
         Why should'st thou, but for some felonious end,
         In thy dark lantern thus close up the stars? --Milton.
   -- Fe*lo"ni*ous*ly, adv. -- Fe*lo"ni*ous*ness, n.
   [1913 Webster]

WordNet (r) 3.0 (2006):

felonious
    adj 1: involving or being or having the nature of a crime; "a
           criminal offense"; "criminal abuse"; "felonious intent"
           [syn: criminal, felonious]