Instrument is brought back by sailor (5)
I believe the answer is:
sitar
'instrument' is the definition.
(sitar is a kind of instrument)
'is brought back by sailor' is the wordplay.
'brought back' says the letters should be written in reverse.
'by' means one lot of letters go next to another.
'sailor' becomes 'tar' (tar is a kind of sailor).
'is' reversed gives 'si'.
'si'+'tar'='SITAR'
(Other definitions for sitar that I've seen before include "Guitar-like instrument" , "Long-necked musical instrument of India" , "music producer" , "Stringed instrument of the subcontinent" , "Astir with Indian long-necked lute" .)