The Collaborative International Dictionary of English v.0.48:

nuclear fusion reaction \nuclear fusion reaction\ n.
   A nuclear reaction in which nuclei combine to form more
   massive nuclei with the simultaneous release of energy.

   Syn: fusion, nuclear fusion.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

nuclear fusion reaction
    n 1: a nuclear reaction in which nuclei combine to form more
         massive nuclei with the simultaneous release of energy
         [syn: fusion, nuclear fusion, nuclear fusion
         reaction]