Small sail turned by bosun evenly (5)
I believe the answer is:
bijou
'small' is the definition.
(I've seen this before)
'sail turned by bosun evenly' is the wordplay.
'sail' becomes 'jib' (jib is a kind of sail).
'turned' is a reversal indicator.
'by' is a charade indicator (letters next to each other).
'evenly' means one should take alternating letters (the letters in even-numbered positions).
The alternate letters of 'bosun' are 'ou'.
'jib' reversed gives 'bij'.
'bij'+'ou'='BIJOU'
(Other definitions for bijou that I've seen before include "Small, but elegant and tasteful" , "Small trinket" , "Jewel" , "Small and delicate" , "Tiny, precious" .)