The Collaborative International Dictionary of English v.0.48:

Univalent \U*niv"a*lent\, a. [Uni- + L. valens, -entis, p. pr.
   See Valence.] (Chem.)
   Having a valence of one; capable of combining with, or of
   being substituted for, one atom of hydrogen; monovalent; --
   said of certain atoms and radicals.
   [1913 Webster]

WordNet (r) 3.0 (2006):

univalent
    adj 1: used of a chromosome that is not paired or united with
           its homologous chromosome during synapsis; "a univalent
           chromosome" [ant: bivalent, double, multivalent]
    2: having a valence of 1 [syn: monovalent, univalent] [ant:
       multivalent, polyvalent]