The Collaborative International Dictionary of English v.0.48:

Transatlantic \Trans`at*lan"tic\ (tr[a^]ns*[a^]t*l[a^]n"t[i^]k),
   a. [Pref. trans- + Atlantic: cf. F. transatlantique.]
   1. Lying or being beyond the Atlantic Ocean.
      [1913 Webster]

   Note: When used by a person in Europe or Africa,
         transatlantic signifies being in America; when by a
         person in America, it denotes being or lying in Europe
         or Africa, especially the former.
         [1913 Webster]

   2. Crossing the Atlantic Ocean; as, a transatlantic flight.
      [1913 Webster +PJC]

WordNet (r) 3.0 (2006):

transatlantic
    adj 1: crossing the Atlantic Ocean; "transatlantic flight"