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]

Moby Thesaurus II by Grady Ward, 1.0:

41 Moby Thesaurus words for "motherhood":
   affiliation, agnation, alliance, ancestry, blood,
   blood relationship, brotherhood, brothership, cognation,
   common ancestry, common descent, connection, consanguinity,
   cousinhood, cousinship, enation, fatherhood, filiation, fraternity,
   kindred, kinship, maternalness, maternity, matrilineage, matriliny,
   matrisib, matrocliny, motherliness, mothership, paternity,
   patrilineage, patriliny, patrisib, patrocliny, propinquity,
   relation, relationship, sibship, sisterhood, sistership,
   ties of blood