1.
pent-up resentment, feeling of vindication
A sense of lingering frustration or resentment that has been building up. Most commonly used in the expression 留飲を下げる, meaning to feel a sense of relief or vindication when a grievance is finally addressed.
Usage
留飲 almost always appears in the set expression 留飲を下げる (to feel vindicated, to have one's frustration relieved). Originally a medical term referring to acid reflux or heartburn, it came to figuratively mean pent-up resentment that is relieved. The word is rarely used outside this fixed phrase.