Naval sword nicked by young woman (7)
I believe the answer is:
cutlass
'naval sword' is the definition.
(I've seen this before)
'nicked by young woman' is the wordplay.
'nicked' becomes 'cut' (nick can mean to cut).
'by' says to put letters next to each other.
'young woman' becomes 'lass' (informal term for a young woman).
'cut'+'lass'='CUTLASS'
(Other definitions for cutlass that I've seen before include "Curved sailors' sword" , "Piratical sword" , "Steel" , "Short, heavy curved sword" , "Pirate's sword" .)