The Collaborative International Dictionary of English v.0.48:

Dastard \Das"tard\, v. t.
   To dastardize. [R.] --Dryden.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Dastard \Das"tard\ (d[a^]s"t[~e]rd), n. [Prob. from Icel.
   d[ae]str exhausted. breathless, p. p. of d[ae]sa to groan,
   lose one's breath; cf. dasask to become exhausted, and E.
   daze.]
   One who meanly shrinks from danger; an arrant coward; a
   poltroon.
   [1913 Webster]

         You are all recreants and dashtards, and delight to
         live in slavery to the nobility.         --Shak.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Dastard \Das"tard\, a.
   Meanly shrinking from danger; cowardly; dastardly. "Their
   dastard souls." --Addison.
   [1913 Webster]

WordNet (r) 3.0 (2006):

dastard
    adj 1: despicably cowardly; "the unprovoked and dastardly attack
           by Japan on...December 7th"- F.D. Roosevelt [syn:
           dastard(a), dastardly]
    n 1: a despicable coward