The Collaborative International Dictionary of English v.0.48:

Motherless \Moth"er*less\, a. [AS. m[=o]dorle['a]s.]
   Destitute of a mother; having lost a mother; as, motherless
   children.
   [1913 Webster]

WordNet (r) 3.0 (2006):

motherless
    adj 1: having no living or known mother

Moby Thesaurus II by Grady Ward, 1.0:

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