Beginning to anticipate win, once more (5)
I believe the answer is:
again
'once more' is the definition.
('again' can be a synonym of 'once more')
'beginning to anticipate win' is the wordplay.
'beginning to' suggests taking the first letters.
'win' becomes 'gain' ('gain' can be a synonym of 'win'**).
The first letter of 'anticipate' is 'a'.
'a'+'gain'='AGAIN'
(Other definitions for again that I've seen before include "second term" , "Repeatedly" , "Here we go ___" , "repeat order" , "Moreover - a second time" .)