Moon to make an attempt at seduction? That's not unknown! (6)
I believe the answer is:
triton
'moon' is the definition.
(I've seen this before)
'to make an attempt at seduction? that's not unknown' is the wordplay.
'to make an attempt at seduction?' becomes 'tryiton' (try it on).
'that's not' is a deletion indicator.
'unknown' becomes 'y' (algebra).
'tryiton' with 'y' taken away is 'TRITON'.
(Other definitions for triton that I've seen before include "Son of Poseidon, shown as man with fish's tail with trident and shell-trumpet" , "conch-blowing deity" , "Greek sea-god like man with fish's tail, trident and shelltrumpet" , "Horn-blower" , "Greek minor sea-god with trident, fish-tail and shell trumpet" .)