Leave a ring on (7)
I believe the answer is:
abandon
'leave' is the definition.
(to abandon is to leave or desert)
'a ring on' is the wordplay.
'ring' becomes 'band' (synonyms).
'a'+'band'+'on'='ABANDON'
(Other definitions for abandon that I've seen before include "Lack of constraint" , "Desert - recklessness" , "Czech city" , "Desert, strand" , "Permanently desert" .)