"Coterminus" is defined as having a common boundary or arriving at the same time or place. Some possible antonyms for this word might include: separate, disparate, divergent, distinct, independent, unrelated, distant, or unconnected. These words all suggest a lack of proximity or connection between two things, as opposed to the closeness or overlap implied by "coterminus." For example, two countries might be separate and distinct, with no common border, while two events might occur independently of each other, without any temporal or geographic overlap. By contrast, "coterminus" implies a shared boundary or simultaneous occurrence.