Co-terminus refers to something that has a common boundary or coincides with another thing. The antonyms for this term may vary depending on the context of usage. For example, antonyms of co-terminus may include unconnected, separate, distinct, or non-overlapping in reference to spatial boundaries. In a temporal sense, antonyms of co-terminus may include non-simultaneous, non-coinciding, or non-parallel. In a more general sense, antonyms of co-terminus may include incongruous, unrelated, dissimilar, or unrelated. The choice of antonym will depend on the intended usage and context of the word co-terminus.