Merriam-Webster Collegiate Dictionary - triton

 I. noun  Etymology: Latin, from Greek Triton  Date: 1536  1. capitalized a son of Poseidon described as a demigod of the sea with the lower part of his body like that of a fish  2. New Latin, genus name, from Latin Triton any of various large marine gastropod mollusks (family Ranellidae syn. Cymatiidae) with a heavy elongated conical shell; also the shell  II. noun  Etymology: tritium + 2-on  Date: 1934 the nucleus of tritium