/tri dak"neuh/ , n.
a genus of giant clams inhabiting reefs in the South Pacific, attaining a diameter of 4 ft. (1.2 m) or more, and weighing over 500 lb. (227 kg).
[ 1770-80; tridacnus requiring three bites trídaknos , equiv. to tri- TRI- + dákn ( ein ) to bite + - os adj. suffix ]