There are various entries for both but for one, Merriam-Webster says that resentment is "a feeling of anger or displeasure about someone or something unfair." For the second word, it says "a strong feeling of anger toward someone that lasts for a long time."
My question is, does "unfairness" play a role in holding a grudge also? And secondly, is the main difference between the two the matter of time or also intensity?
For instance, let's say a neighbor makes noises at night, I might be angry and if I feel it's unfair that they do that and I can't or that the building manager doesn't care, I assume that's resentment. But what makes it a grudge? Is it related to it happening often? To my resentment being real intense and not being able to forgive them?
Thanks.
Best Answer
You can think of grudge as a hypernym of resentment.
A grudge need not be the result of (perceived) unfairness; it can just result from (violation of) the holder's vested interests irrespective of the fairness involved. Also, a grudge is always directed towards people (I haven't seen otherwise).
A resentment on the other hand (as you said) results from a perceived unfairness. A resentment, unlike a grudge, can be directed towards concepts (like policies and laws) in addition to people.
Definitions from M-W to conclude:
Note from the examples:
The grudge does not necessarily mean that the boss was unfair.
The resentment is directed at policies.