Tense victory secures double (4)
I believe the answer is:
twin
'double' is the definition.
(twin can mean someone's double)
'tense victory' is the wordplay.
'tense' becomes 't' (grammatical abbreviation).
'victory' becomes 'win' (a win is a victory).
't'+'win'='TWIN'
'secures' acts as a link.
(Other definitions for twin that I've seen before include "One of a similar pair" , "One of two conceived simultaneously" , "One of a matching pair" , "One of two conceived together" , "Lookalike" .)