Not a good sailor (6)
I believe the answer is:
pirate
'sailor' is the definition.
(I've seen this before)
'not a good' is the wordplay.
I cannot really see how this works, but
'a' is found in the answer.
'good' could be 'pi' (old-fashioned term for pious) and 'pi' is present in the answer.
The remaining letters 'rte' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for pirate that I've seen before include "Seaborne robber" , "Illegally-copied (version)" , "plagiarist" , "Criminal on the high seas" , "Hook", for example" .)