Perfect beau lost game (8)
I believe the answer is:
absolute
'perfect' is the definition.
(synonyms)
'beau lost game' is the wordplay.
'game' is an anagram indicator (a game or puzzle of the letters).
'beau'+'lost'='beaulost'
'beaulost' anagrammed gives 'ABSOLUTE'.
(Other definitions for absolute that I've seen before include "Complete or unconditional" , "for certain" , "Unrestricted, out-and-out" , "Not subject to limitation" , "Unlimited; not relative" .)