Triton

Meaning uncertain. It is possibly related to a root meaning "the sea" (cognate with Old Irish trethan). Alternatively it could be connected to Greek τρεῖς (treis) meaning "three" (ordinal form τρίτος). In Greek mythology Triton was the son of Poseidon and Amphitrite. He was often depicted as a merman, half-human and half-fish. The largest of Neptune's moons is named after him.