The Collaborative International Dictionary of English v.0.48:

Fatherless \Fa"ther*less\, a.
   1. Destitute of a living father; as, a fatherless child.
      [1913 Webster]

   2. Without a known author. --Beau. & Fl.
      [1913 Webster]

WordNet (r) 3.0 (2006):

fatherless
    adj 1: having no living father
    2: not having a known or legally responsible father

Moby Thesaurus II by Grady Ward, 1.0:

34 Moby Thesaurus words for "fatherless":
   abandoned, aidless, baseborn, bastard, bereaved, bereft,
   defenseless, deprived, deserted, desolate, forlorn, forsaken,
   friendless, godforsaken, guideless, helpless, homeless, kithless,
   leaderless, misbegotten, motherless, natural, orphan, orphaned,
   outcast, parentless, pregnable, spurious, supposititious,
   unfriended, unprotected, untenable, vulnerable, widowed