Couple close to significant victory (4)
I believe the answer is:
twin
'couple' is the definition.
(I know that couple can be written as twin)
'close to significant victory' is the wordplay.
'close to' says to take the final letters (the close of something is the end).
'victory' becomes 'win' (a win is a victory).
The final letter of 'significant' is 't'.
't'+'win'='TWIN'
(Other definitions for twin that I've seen before include "One from double birth" , "Make association" , "One of two born together" , "Dead ringer" , "Very much like" .)