Entry 1 sense Webster, 1913 Sea colander /sē käl'-ən-dẽr/ · Sea· col·an·der · IPA 01 A large blackfish seaweed (Agarum Turneri), the frond of which is punctured with many little holes. 1. A large blackfish seaweed (Agarum Turneri), the frond of which is punctured with many little holes.(Bot.)