The Collaborative International Dictionary of English v.0.48:

Atlantic \At*lan"tic\, a. [L. Atlanticus, fr. Atlas. See Atlas
   and Atlantes.]
   1. Of or pertaining to Mt. Atlas in Libya, and hence applied
      to the ocean which lies between Europe and Africa on the
      east and America on the west; as, the Atlantic Ocean
      (called also the Atlantic); the Atlantic basin; the
      Atlantic telegraph.
      [1913 Webster]

   2. Of or pertaining to the isle of Atlantis.
      [1913 Webster]

   3. Descended from Atlas.
      [1913 Webster]

            The seven Atlantic sisters.           --Milton.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Atlantic
    adj 1: relating to or bordering the Atlantic Ocean; "Atlantic
           currents"
    n 1: the 2nd largest ocean; separates North and South America on
         the west from Europe and Africa on the east [syn:
         Atlantic, Atlantic Ocean]