bite down on (something)

1. To bite very hard and purposefully on something. I nearly lost a tooth biting down on that apple! She bit down on the man's hand to get him to let go of her. As soon as she bit down on her sandwich, her loose tooth came out!

2. To repress or hold back something, especially an emotion. I bit down on the rude comments that were dancing at the tip of my tongue. She had to keep biting down on her anger as the CEO continued to discredit her work. I had to bite down on a snarky remark as my sister gushed about her new boyfriend.