The Collaborative International Dictionary of English v.0.48:

Jointure \Join"ture\, n. [F. jointure a joint, orig., a joining,
   L. junctura, fr. jungere to join. See Join, and cf.
   Juncture.]
   [1913 Webster]
   1. A joining; a joint. [Obs.]
      [1913 Webster]

   2. (Law) An estate settled on a wife, which she is to enjoy
      after husband's decease, for her own life at least, in
      satisfaction of dower.
      [1913 Webster]

            The jointure that your king must make,
            Which with her dowry shall be counterpoised. --Shak.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Jointure \Join"ture\, v. t. [imp. & p. p. Jointured; p. pr. &
   vb. n. Jointuring.]
   To settle a jointure upon.
   [1913 Webster]

WordNet (r) 3.0 (2006):

jointure
    n 1: (law) an estate secured to a prospective wife as a marriage
         settlement in lieu of a dower [syn: jointure, legal
         jointure]
    2: the act of making or becoming a single unit; "the union of
       opposing factions"; "he looked forward to the unification of
       his family for the holidays" [syn: union, unification,
       uniting, conjugation, jointure] [ant: disunion]