Moon of Neptune (6)
I believe the answer is:
triton
'moon of neptune' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for triton that I've seen before include "heavenly conch-blower" , "Greek sea-god like man with fish's tail, trident and shelltrumpet" , "Minor Greek god" , "conch-blowing deity" , "Moon" .)