The Collaborative International Dictionary of English v.0.48:

Beltane \Bel"tane\, n. [Gael. bealltainn, bealltuinn.]
   [1913 Webster]
   1. The first day of May (Old Style).
      [1913 Webster]

            The quarter-days anciently in Scotland were
            Hallowmas, Candlemas, Beltane, and Lammas. --New
                                                  English Dict.
      [1913 Webster]

   2. A festival of the heathen Celts on the first day of May,
      in the observance of which great bonfires were kindled. It
      still exists in a modified form in some parts of Scotland
      and Ireland.
      [1913 Webster]