The Collaborative International Dictionary of English v.0.48:

Ganancial \Ga*nan"cial\, a. [Sp., pertaining to gain, held in
   common, fr. ganancia gain.] (Law)
   Designating, pertaining to, or held under, the Spanish system
   of law (called

   ganancial system) which controls the title and disposition
      of the property acquired during marriage by the husband or
      wife.
      [Webster 1913 Suppl.]

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

GANANCIAL, Spanish law. A term which in Spanish signifies nearly the same as
acquets. Bienes gananciales are thus defined: " Aquellos que el marido y la
mujer o cualquiera de los dos adquieren o aumentan durante el matrimonio por
compra o otro contrato, 6 mediante su trabajo e industria, como tambien los
frutos de los bienos proprios que cada uno elevo al matrimonio, et de los
que subsistiendo este adquieran para si por cualquier titulo." 1 Febr. Nov.
lib. 1, tit. 2, c. 8, s. 1. This is a species of community; the property of
which it is formed belongs in common to the two consorts, and, on the
dissolution of the marriage, is divisible between them in equal shares. It
is confined to their future acquisition durante el matrimonio, and the
frutos, or rents and profits of the other property. 1 Burge on Confl. of
Laws, 418, 419; Aso & Man. Inst. B. 1, t. 7, c. 5, Sec. 1.