- (North American English also sea turtle)
a large reptile with a hard round shell that lives in the sea 海龟 
- (North American English, informal)
any reptile with a large shell, for example a tortoise or terrapin （任何种类的）龟；陆龟；水龟；鳖
Word Originmid 16th cent.: apparently an alteration of French tortue, from medieval Latin tortuca, of uncertain origin.
Idioms
turn turtle
(of a boat 船 to turn over completely while sailing （在航行中）倾覆，翻