Execute British boss in possession of ecstasy (6)
I believe the answer is:
behead
'execute' is the definition.
(I know that behead is a more specific form of the action execute)
'british boss in possession of ecstasy' is the wordplay.
'british' becomes 'b' (abbreviation e.g. in BBC).
'boss' becomes 'head' (synonyms).
'in possession of' means one lot of letters goes inside another (has inside).
'ecstasy' becomes 'E' (informal term for the drug).
'b'+'head'='bhead'
'bhead' enclosing 'e' is 'BEHEAD'.
(Other definitions for behead that I've seen before include "Decapitate" , "wield the axe" , "Remove cranium as in old execution" , "Carry out execution" , "Guillotine" .)