Uncertain given war when beaten (8)
I believe the answer is:
wavering
'uncertain' is the definition.
(thesaurus)
'given war when beaten' is the wordplay.
'when beaten' is an anagram indicator (letters beaten into a new form).
'given'+'war'='givenwar'
'givenwar' anagrammed gives 'WAVERING'.
(Other definitions for wavering that I've seen before include "About to change mind" , "'Uncertain, hesitating (8)'" , "Beginning to weaken" , "Vacillating" , "Faltering" .)