The Collaborative International Dictionary of English v.0.48:

Gael \Gael\, n.sing. & pl. [See Gaelic.] (Ethnol.)
   A Celt or the Celts of the Scotch Highlands or of Ireland;
   now esp., a Scotch Highlander of Celtic origin.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Gael
    n 1: a Gaelic-speaking Celt in Ireland or Scotland or the Isle
         of Man