The Collaborative International Dictionary of English v.0.48:

jumbo jet \jum"bo jet`\ (j[u^]m"b[-o] j[e^]t`), n.
   A large commercial jet airplane, usually having a passenger
   capacity of over 300 in normal use; also called widebody
   airplane.
   [PJC]

WordNet (r) 3.0 (2006):

jumbo jet
    n 1: a very large jet plane [syn: jumbojet, jumbo jet]