Bitterness in Shakespeare on his deathbed, possibly?
I believe the answer is:
ill will
'bitterness' is the definition.
(thesaurus)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for ill will that I've seen before include "Hostility, malevolence" , "Disposition of enemy" , "Positively unfriendly disposition" , "Hostile and unkind feeling" , "causing resentment" .)