Former lead in Hamlet, one with part in show (7)
I believe the answer is:
exhibit
'show' is the definition.
(I know that show can be written as exhibit)
'former lead in hamlet one with part' is the wordplay.
'former' becomes 'ex' (prefix meaning former or onetime).
'lead in' suggests taking the first letters.
'one' becomes 'i' (Roman numeral).
'with' says to put letters next to each other.
'part' becomes 'bit' (both mean a piece of something).
The first letter of 'hamlet' is 'h'.
'ex'+'h'+'i'+'bit'='EXHIBIT'
'in' is the link.
(Other definitions for exhibit that I've seen before include "Something on show" , "Show - piece of evidence in court" , "Object on formal public display" , "Give public show, as of paintings" , "Manifest" .)