Source : Webster's Revised Unabridged Dictionary (1913)

Dastardly \Das"tard*ly\, a.
   Meanly timid; cowardly; base; as, a dastardly outrage.

Source : WordNet®

dastardly
     adj : treacherously cowardly; "the unprovoked and dastardly attack
           by Japan on...December 7th"- F.D. Roosevelt [syn: {dastard(a)}]