Drug of French worker containing iron? (10)
I believe the answer is:
depressant
'drug' is the definition.
(I know that depressant is a type of drug of abuse)
'of french worker containing iron?' is the wordplay.
'of french' becomes 'de' ('of' in French).
'worker' becomes 'ant' (worker is a type of ant).
'containing' indicates putting letters inside.
'iron?' becomes 'press' (ironing is a kind of pressing).
'de'+'ant'='deant'
'deant' going around 'press' is 'DEPRESSANT'.
(Other definitions for depressant that I've seen before include "Drug reducing nervous activity" , "reducing activity of vital functions" , "Sedative drug" , "Downer" , "Lowering spirits" .)