in Latin, the form of com- "together, with" in compounds with stems beginning in vowels, h-, and gn-; see com-. Taken in English from 17c. as a living prefix meaning "together, mutually, in common," and used promiscuously with native words (co-worker) and Latin-derived words not beginning with vowels (codependent), including some already having it (co-conspirator).
mid-15c., "relating to or marking boundaries," from Latin terminalis "pertaining to a boundary or end, final," from terminus "end, boundary line" (see terminus). Meaning "fatal" (terminal illness) is first recorded 1891. Sense of "situated at the extreme end" (of something) is from 1805. Slang meaning "extreme" first recorded 1983. Related: Termninally.
"having the same limit, touching at the boundary," 1670s, from Latin conterminus "bordering upon, having a common boundary," from assimilated form of com "together, with" (see con-) + terminus "end, boundary line" (see terminus). Related: Conterminously; conterminousness.
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Harper, D. (n.d.). Etymology of coterminous. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/coterminous