The Collaborative International Dictionary of English v.0.48:

pact \pact\ (p[a^]kt), n. [L. pactum, fr. paciscere to make a
   bargain or contract, fr. pacere to settle, or agree upon; cf.
   pangere to fasten, Gr. phgny`nai, Skr. p[=a][,c]a bond, and
   E. fang: cf. F. pacte. Cf. Peace, Fadge, v.]
   An agreement; a league; a compact; a covenant. --Bacon.
   [1913 Webster]

         The engagement and pact of society which goes by the
         name of the constitution.                --Burke.
   [1913 Webster]

WordNet (r) 3.0 (2006):

pact
    n 1: a written agreement between two states or sovereigns [syn:
         treaty, pact, accord]