Arrest new sailor (3)
I believe the answer is:
nab
'arrest' is the definition.
(I know that arrest can be written as nab)
'new sailor' is the wordplay.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'sailor' becomes 'ab' (abbreviation for able seaman).
'n'+'ab'='NAB'
(Other definitions for nab that I've seen before include "Arrest (colloq.)" , "Seize quickly" , "Pinch" , "Apprehend" , "Collar (sl.)" .)