Shakespeare's Athenian gets in some element (8)
I believe the answer is:
antimony
'element' is the definition.
(antimony is a kind of element)
'shakespeare's athenian gets in some' is the wordplay.
'shakespeare's athenian' becomes 'timon' (I've seen this before).
'gets in' indicates putting letters inside.
'some' becomes 'any' ('any' can be similar in meaning to 'some').
'timon' placed into 'any' is 'ANTIMONY'.
(Other definitions for antimony that I've seen before include "Semimetallic element" , "Brittle element" , "One element" , "Toxic metallic element used in semiconductors" , "Bluish-white element, symbol Sb" .)