Wanting to include element (3)
I believe the answer is:
tin
'element' is the definition.
(tin is a kind of element)
'wanting to include' is the wordplay.
'to include' indicates a hidden word.
'TIN' is hidden within 'wanting'.
(Other definitions for tin that I've seen before include "Element, symbol Sn" , "Kind of metal often used as food container" , "With copper, makes bronze" , "Canister" , "1 down, symbol Sn" .)