Common foil contains aluminium (9)
I believe the answer is:
prevalent
'common' is the definition.
(prevalent can mean common or widespread)
'foil contains aluminium' is the wordplay.
'foil' becomes 'prevent' (I've seen this in another clue).
'contains' is an insertion indicator.
'aluminium' becomes 'al' (Al is the chemical symbol for aluminium).
'prevent' going around 'al' is 'PREVALENT'.
(Other definitions for prevalent that I've seen before include "Ruling" , "powerful" , "Widespread - current" , "general" , "Widely accepted" .)