The Collaborative International Dictionary of English v.0.48:

Poltroon \Pol*troon"\, n. [F. poltron, from It. poltrone an idle
   fellow, sluggard, coward, poltro idle, lazy, also, bed, fr.
   OHG. polstar, bolstar, cushion, G. polster, akin to E.
   bolster. See Bolster.]
   An arrant coward; a dastard; a craven; a mean-spirited
   wretch. --Shak.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Poltroon \Pol*troon"\, a.
   Base; vile; contemptible; cowardly.
   [1913 Webster]

WordNet (r) 3.0 (2006):

poltroon
    adj 1: characterized by complete cowardliness
    n 1: an abject coward [syn: poltroon, craven, recreant]

Moby Thesaurus II by Grady Ward, 1.0:

21 Moby Thesaurus words for "poltroon":
   arrant coward, base, caitiff, chicken, coward, craven, dastard,
   dastardly, dunghill, dunghilly, funk, funker, gutless,
   lily-livered, poltroonish, pusillanimous, quitter, recreant, sneak,
   spunkless, unmanly