The phrase "between us" is commonly used to describe something that is shared or kept confidential by a select group of people. Some synonyms for this phrase can include "confidentially," "privately," "secretly," or "exclusively." These words all convey the idea that there is something that is understood or known by a limited group, and not necessarily meant for public consumption. Other possible synonyms can include "amidst," "among," or "in the midst of," which suggest a sense of being in the middle of an experience or situation. Regardless of the specific synonym used, the phrase "between us" often refers to a special bond or understanding shared between people.