IPA: /ræŋˈkɔrəsli/
KK: /ræŋˈkɔrəsli/
In a way that shows deep-seated bitterness or resentment.
The two politicians argued rancorously during the debate.
Rancorously → It is formed from "rancor" (from Latin "rancorem", meaning bitterness or resentment) and the suffix "-ously" (meaning in a manner characterized by). The word "rancorously" means in a manner characterized by bitterness or deep-seated resentment.
Think of 'rancor' as representing deep bitterness, and remember that 'rancorously' describes behaving in a way that shows that bitterness.