The phrase "through thick and thin" means to stick together through good times and bad times. Synonyms for this phrase include "in good times and bad," "in sickness and in health," and "through ups and downs." Other related phrases include "ride out the storm," "stay the course," "stand by each other," and "never give up." These expressions all convey the idea of unwavering loyalty and commitment, even in the face of adversity. Knowing these synonyms can help you communicate your steadfastness and devotion in a more eloquent and nuanced way.