Queens, say, adopting small sheds (5)
I believe the answer is:
casts
'sheds' is the definition.
('cast' can be a synonym of 'shed')
'queens say adopting small' is the wordplay.
'queens say' becomes 'cats' (queen is a kind of cat).
'adopting' means one lot of letters goes inside another.
'small' becomes 's' (abbreviation - e.g. clothes size).
'cats' enclosing 's' is 'CASTS'.
(Other definitions for casts that I've seen before include "Assigns an actor to a role" , "Allocates parts" , "Eg puts" , "groups of actors" , "Throws" .)