Function of control experiment? (4)
I believe the answer is:
role
'function' is the definition.
(I know that function can be written as role)
'of control experiment?' is the wordplay.
'of' indicates the answer is hidden within the clue.
'ROLE' can be found hidden inside 'control experiment'.
(Other definitions for role that I've seen before include "A part of lore" , "Function in life" , "Playing part" , "Acting part" , "Actor's part" .)