The Collaborative International Dictionary of English v.0.48:

major premise \major premise\ n. (Logic),
   That premise of a syllogism that contains the major term
   (which is the predicate of the conclusion). Contrasted to
   minor premise.
   [WordNet 1.5]

WordNet (r) 3.0 (2006):

major premise
    n 1: the premise of a syllogism that contains the major term
         (which is the predicate of the conclusion) [syn: major
         premise, major premiss]