The Collaborative International Dictionary of English v.0.48:

Motherhood \Moth"er*hood\, n.
   The state of being a mother; the character or office of a
   mother.
   [1913 Webster]

WordNet (r) 3.0 (2006):

motherhood
    n 1: the kinship relation between an offspring and the mother
         [syn: motherhood, maternity]