Collins Chinese Dictionary Plus (3rd edition), 2011:
耿耿于(於)怀(懷) gěnggěng yú huái dwell on
- 她对(對)同事的话(話)一直耿耿于(於)怀(懷)。 Tā duì tóngshì de huà yīzhí gěnggěng yú huái. She kept dwelling on what her colleague had said.