Sailor leaving American navy joint (4)
I believe the answer is:
seam
'joint' is the definition.
(seam is a kind of joint)
'sailor leaving american navy' is the wordplay.
I cannot really see how this works, but
'american' could be 'am' (abbreviation in some contexts) and 'am' is found in the answer.
The remaining letters 'se' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for seam that I've seen before include "Stitched joint" , "Stratum (of a mineral)" , "Fabric joint" , "Join round cricket ball" , "Underground layer of mineral" .)