Rancorous
/ˈræŋkərəs/
Definition 1 of 1
Pro Tip 1/3Long-lasting anger
The word emphasizes that the anger isn't short-lived but continues for a long time, often unnecessarily. 
His rancorous feelings toward his rival lasted for years after the competition.
Pro Tip 2/3Intensity of resentment
'Rancorous' indicates a very strong and deep form of resentment that is more intense than just being annoyed or upset. 
The rancorous relationship between the two colleagues affected the entire office environment.
Pro Tip 3/3Negative debates
Often used to describe debates or arguments where there is more personal animosity than constructive discussion. 
The town hall meeting turned into a rancorous exchange of accusations.