Seamen reflecting at home drink no alcohol (7)
I believe the answer is:
abstain
'drink no alcohol' is the definition.
'seamen reflecting at home' is the wordplay.
'seamen' becomes 'abs' (AB is a naval abbreviation for able seaman).
'reflecting' says the letters should be written backwards.
'home' becomes 'in' ('he's home' can mean 'he's in').
'at' reversed gives 'ta'.
'abs'+'ta'+'in'='ABSTAIN'
(Other definitions for abstain that I've seen before include "Give up smoking, say" , "Don't indulge" , "Hold off" , "Do without, as in lent" , "Don't vote" .)