The phrase "grit one's teeth" expresses an act of determination or endurance in the face of hardship or pain. Other synonyms that can be used to convey a similar meaning include "clench one's jaw," "tighten one's fists," "bear down," "hunker down," and "steel oneself." These phrases all convey a sense of resolve in the face of adversity, and can be used to inspire and motivate action. When faced with challenges, it is important to draw upon our inner strength and resilience, and to find ways to persevere and overcome obstacles. Using these synonyms can help us to communicate these ideas effectively to others.