I join men in skilful scientific test (10)
I believe the answer is:
experiment
'scientific test' is the definition.
'experiment' can be an answer for 'test' (I've seen this before). I'm not certain of the 'scientific' bit.
'i join men in skilful' is the wordplay.
'join' says to put letters next to each other.
'in' is an insertion indicator.
'skilful' becomes 'expert' (synonyms).
'i'+'men'='imen'
'imen' placed within 'expert' is 'EXPERIMENT'.
Can you help me to learn more?
(Other definitions for experiment that I've seen before include "Controlled test" , "Trial" , "scientific investigation" .)