Source : Webster's Revised Unabridged Dictionary (1913)

Tern \Tern\ (t[~e]rn), n. [Dan. terne, t[ae]rne; akin to Sw.
   t["a]rna, Icel. [thorn]erna; cf. NL. sterna.] (Zo["o]l.)
   Any one of numerous species of long-winged aquatic birds,
   allied to the gulls, and belonging to {Sterna} and various
   allied genera.

   Note: Terns differ from gulls chiefly in their graceful form,
         in their weaker and more slender bills and feet, and
         their longer and more pointed wings. The tail is
         usually forked. Most of the species are white with the
         back and wings pale gray, and often with a dark head.
         The common European tern ({Sterna hirundo}) is found
         also in Asia and America. Among other American species
         are the arctic tern ({S. paradis[ae]a}), the roseate
         tern ({S. Dougalli}), the least tern ({S. Antillarum}),
         the royal tern ({S. maxima}), and the sooty tern ({S.
         fuliginosa}).

   {Hooded tern}. See {Fairy bird}, under {Fairy}.

   {Marsh tern}, any tern of the genus {Hydrochelidon}. They
      frequent marshes and rivers and feed largely upon insects.
      

   {River tern}, any tern belonging to {Se["e]na} or allied
      genera which frequent rivers.

   {Sea tern}, any tern of the genus {Thalasseus}. Terns of this
      genus have very long, pointed wings, and chiefly frequent
      seas and the mouths of large rivers.

Source : WordNet®

Sterna hirundo
     n : common tern of Eurasia and America having white black and
         gray plumage [syn: {sea swallow}]