\Con*cu"bi*nage\, n.
1. The cohabiting of a man and a woman who are not legally
   married; the state of being a concubine.
Note: In some countries, concubinage is marriage of an
      inferior kind, or performed with less solemnity than a
      true or formal marriage; or marriage with a woman of
      inferior condition, to whom the husband does not convey
      his rank or quality. Under Roman law, it was the living
      of a man and woman in sexual relations without
      marriage, but in conformity with local law.
2. (Law) A plea, in which it is alleged that the woman suing
   for dower was not lawfully married to the man in whose
   lands she seeks to be endowed, but that she was his
   concubine.