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]