Expert male in criminal trial (12)
I believe the answer is:
experimental
'trial' is the definition.
(synonyms)
'expert male in criminal' is the wordplay.
'criminal' indicates an anagram.
'expert'+'male'+'in'='expertmalein'
'expertmalein' is an anagram of 'EXPERIMENTAL'.
(Other definitions for experimental that I've seen before include "Based on untested ideas" , "test" , "Undergoing tests" , "Exploratory" , "Relating to laboratory investigation" .)