Sober sailors shelter crossing current (9)
I believe the answer is:
abstinent
'sober' is the definition.
(similar in meaning)
'sailors shelter crossing current' is the wordplay.
'sailors' becomes 'abs' (AB is short for able seaman).
'shelter' becomes 'tent' (canvas shelter).
'crossing' means one lot of letters goes inside another (to cross can mean to go over or around).
'current' becomes 'in' ('in' can mean current or trendy).
'tent' going around 'in' is 'tinent'.
'abs'+'tinent'='ABSTINENT'
(Other definitions for abstinent that I've seen before include "without booze" , "Going without, especially food and alcohol" , "Avoiding alcohol" , "nowhere near the drink" , "Keeping off alcohol" .)