The Collaborative International Dictionary of English v.0.48:

Precontract \Pre`con*tract"\, v. i.
   To make a previous contract or agreement. --Ayliffe.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Precontract \Pre*con"tract\, n.
   A contract preceding another; especially (Law), a contract of
   marriage which, according to the ancient law, rendered void a
   subsequent marriage solemnized in violation of it. --Abbott.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Precontract \Pre`con*tract"\, v. t. [imp. & p. p.
   Precontracted; p. pr. & vb. n. Precontracting.]
   To contract, engage, or stipulate previously.
   [1913 Webster]

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

PRECONTRACT. An engagement entered into by a person, which renders him
unable to enter into another; as a promise or covenant of marriage to be had
afterwards. When made per verba de presenti, it is in fact a marriage, and
in that case the party making it cannot marry another person.