Island people in specialist trial (10)
I believe the answer is:
experiment
'trial' is the definition.
(synonyms)
'island people in specialist' is the wordplay.
'island' becomes 'i'.
'people' becomes 'men' (men can refer to humanity as a whole).
'in' is an insertion indicator.
'specialist' becomes 'expert' (a specialist is an expert in a field).
'i'+'men'='imen'
'imen' going into 'expert' is 'EXPERIMENT'.
(Other definitions for experiment that I've seen before include "Controlled test" , "Trial" , "scientific investigation" .)