The Collaborative International Dictionary of English v.0.48:

Curtesy \Cur"te*sy\ (k?r"t?-s?), n.; pl. Curtesies (-s?z).
   [Either fr. courlesy, the lands being held as it were by
   favor; or fr. court (LL. curtis), the husband being regarded
   as holding the lands as a vassal of the court. See Court,
   Courtesy.] (Law)
   the life estate which a husband has in the lands of his
   deceased wife, which by the common law takes effect where he
   has had issue by her, born alive, and capable of inheriting
   the lands. --Mozley & W.
   [1913 Webster]

Bouvier's Law Dictionary, Revised 6th Ed (1856):

CURTESY, or COURTESY, Scotch law. A life-rent given by law to the surviving
husband, of all his wife's heritage of which she died intest, if there was a
child of the marriage born alive. The child born of the marriage must be the
mother's heir. If she had a child by a former marriage, who is to succeed to
her estate, the husband has no right to the curtesy while such child is
alive; so that the curtesy is due to the husband rather as father to the
heir, than as husband to an heiress, conformable to the Roman law, which
gives to the father the usufruct of what the child succeeds to by the
mother. Ersk. Pr. L. Scot. B. 2, t. 9, s. 30. Vide Estate by the curtesy.