Dismissed one side entirely (8)
I believe the answer is:
outright
'entirely' is the definition.
(thesaurus)
'dismissed one side' is the wordplay.
'dismissed' becomes 'out' (I've seen this before).
'one side' becomes 'right' (I've seen this before**).
'out'+'right'='OUTRIGHT'
(Other definitions for outright that I've seen before include "without qualifications" , "Completely - undisputed" , "Without reservation or exception" , "Without reservation or stipulation" , "Altogether; openly" .)