Cheers on cheers reflected popular win (6)
I believe the answer is:
attain
'win' is the definition.
(attain can mean to win or secure)
'cheers on cheers reflected popular' is the wordplay.
'cheers' becomes 'ta' (both can mean thank you).
'on' is a charade indicator (letters next to each other).
'cheers' becomes 'ta' (both can mean thank you).
'reflected' says the letters should be written in reverse (letters reflected back).
'popular' becomes 'in' ('in' can mean trendy).
'ta' back-to-front is 'at'.
'ta' put after 'at' is 'atta'.
'atta'+'in'='ATTAIN'
(Other definitions for attain that I've seen before include "Arrive at or achieve" , "Succeed in reaching, achieve" , "Reach (age, size etc.)" , "Reach (a specified age)" , "Reach or accomplish" .)