'Tern' definitions:

Definition of 'tern'

noun

Small slender gull having narrow wings and a forked tail

From: GCIDE

Tern \Tern\ (t[~e]rn), n. [Dan. terne, t[ae]rne; akin to Sw. t[aum]rna, Icel. [thorn]erna; cf. NL. sterna.] (Zool.) Any one of numerous species of long-winged aquatic birds, allied to the gulls, and belonging to Sterna and various allied genera. [1913 Webster]
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 (Sterna paradisaea), the roseate tern (Sterna Dougalli), the least tern ({Sterna Antillarum}), the royal tern (Sterna maxima), and the sooty tern (Sterna fuliginosa). [1913 Webster]
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 Seena 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. [1913 Webster]

From: GCIDE

Tern \Tern\, a. [L. pl. terni three each, three; akin to tres three. See Three, and cf. Trine.] Threefold; triple; consisting of three; ternate. [1913 Webster]
Tern flowers (Bot.), flowers growing three and three together.
Tern leaves (Bot.), leaves arranged in threes, or three by three, or having three in each whorl or set.
Tern peduncles (Bot.), three peduncles growing together from the same axis.
Tern schooner (Naut.), a three-masted schooner. [1913 Webster]

From: GCIDE

Tern \Tern\, n. [F. terne. See Tern, a.] That which consists of, or pertains to, three things or numbers together; especially, a prize in a lottery resulting from the favorable combination of three numbers in the drawing; also, the three numbers themselves. [1913 Webster]
She'd win a tern in Thursday's lottery. --Mrs. Browning. [1913 Webster]