Miss Shakespearean title role -— endlessly upset (4)
I believe the answer is:
omit
'miss' is the definition.
(synonyms)
'shakespearean title role endlessly upset' is the wordplay.
'shakespearean title role' becomes 'timon' (title role in the Shakespeare play Timon of Athens).
'endlessly' means to remove the last letter.
'upset' shows that the letters should be reversed in order.
'timon' with its final letter removed is 'timo'.
'timo' written backwards gives 'OMIT'.
(Other definitions for omit that I've seen before include "Leave out or forget" , "Leave something out" , "Fail (to do something)" , "Leave out, do not include (4)" , "Miss out" .)