Concomitance is a term used to describe the COEXISTENCE of two or more things. It is often used to describe the relationship between two or more events, ideas, or people. COEXISTENCE is an 11-letter word that is closely related to concomitance, and it means the simultaneous existence of two or more things. This term is often used to describe the relationship between two or more entities that are not necessarily in conflict with each other.