adjective (a)

• used of a chromosome that is not paired or united with its homologous chromosome during synapsis(adj.all)

  Example:
  A univalent chromosome.
  

  Antonym:
  bivalent, double
  

  source: wordnet30
• having a valence of 1(adj.all)

  Synonym:
  monovalent
  Antonym:
  multivalent, polyvalent
  

  source: wordnet30
• 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.(adjective)

  source: webster1913