Single people in skilful trial (10)
I believe the answer is:
experiment
'trial' is the definition.
(I've seen this before)
'single people in skilful' is the wordplay.
'single' becomes 'i' (one).
'people' becomes 'men' (man is a kind of person).
'in' is an insertion indicator.
'skilful' becomes 'expert' ('expert' can be a synonym of 'skilful'**).
'i'+'men'='imen'
'imen' inserted into 'expert' is 'EXPERIMENT'.
(Other definitions for experiment that I've seen before include "Trial" , "scientific investigation" , "Controlled test" .)