Sober sailors can repair net (9)
I believe the answer is:
abstinent
'sober' is the definition.
(similar in meaning)
'sailors can repair net' is the wordplay.
'sailors' becomes 'abs' (AB is short for able seaman).
'can' becomes 'tin' (synonyms).
'repair net' becomes 'ent' (I can't justify this - if you can you should give a lot more credence to this answer).
'abs'+'tin'+'ent'='ABSTINENT'
(Other definitions for abstinent that I've seen before include "Forsaking alcohol" , "Avoiding port, perhaps" , "nowhere near the drink" , "self-restraint" , "Keeping off alcohol" .)