Coexistence is the noun: the state of two different things, or two groups of people, existing together at the same time or in the same place. You will often see it with peaceful: "peaceful coexistence" means living side by side without war. That phrase became famous in politics, when big countries talked about not destroying each other. Without "peaceful," coexistence is more neutral — it can be uneasy. Two people in a family can be in coexistence and still argue every night. Though actually, many writers still use the bare word as if it already meant "getting along." Listen for the adjectives around it.