I am under the impression that both coterminous and conterminous have exactly the same meaning. There was a remark that Latin purists prefer conterminous. Why?

Is there any significant difference between the two? Do co- and con- have same effect on words?

I am looking for any additional information about these two words which would help me understand them better.

3 Answers 3


Yes, conterminous and coterminous both mean "to share a boundary".

According to the entries for co- and con-, below, co- is an Anglicising of con-, which is possibly why Latin purists prefer con-

In this instance co- and con- both mean together or with.

Etymology of co-

in Latin, the form of com- in compounds with stems beginning in vowels and 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 and Latin-derived words not beginning with vowels, sometimes even with words already having it (e.g. co-conspiritor).

Etymology of con-

prefix meaning "together, with," sometimes merely intensive; the form of com- used in Latin before consonants except -b-, -p-, -l-, -m-, or -r-. In native English formations, co- tends to be used where Latin would use con- (e.g. costar).

  • 1
    So the semantic fields of these words are coterminous.
    – bdsl
    Sep 23, 2015 at 13:26
  • "Sharing a boundary" is ambiguous as used in common English. Does it mean to share a boundary as in two states sharing a river as a boundary, i.e., a partial bounds? Or does it mean to share the entire boundary? The latter excludes California and Nevada in the US sharing a boundary, while the former does not. In fact, this is what co- vs con-terminous seem to differentiate. May 20, 2022 at 12:26

Dictionary.com disagrees with the currently accepted answer. It lists "coterminous" as one of the possible meanings of "conterminous", but also two other meanings.

Its definitions of "coterminous":

  1. having the same border or covering the same area.
  2. being the same in extent; coextensive in range or scope.

Its definitions of "conterminous":

  1. having a common boundary; bordering; contiguous.
  2. meeting at the ends; without an intervening gap:
    In our calendar system, the close of one year is conterminous with the beginning of the next.
  3. coterminous.

Indeed, the National Geographic Style Guide says to use "conterminous" for the 48 contiguous states of the U.S.; that fits with definition 1 for "conterminous" and not with either of the definitions for "coterminous".

  • I tend to agree with you/dictionary.com. I am still confused, though. Are Montana and North Dakota co/conterminous because they share the 49th parallel with Canada? Or are they co/conterminous with each other, because they meet at their respective east/west ends? Is DE co/conterminous with NJ because they share a border via Delaware River, and that they share PA as a border, but in either case each do not touch the other? There seems to be times where Co- and Con- are synonymous, but are there times where one can be co- but not con-, or vice-versa.
    – Andrew Jay
    Dec 28, 2023 at 16:33

"Con-" has the meaning of :

used with certain words to add a notion similar to those conveyed by with, together, or joint congenial, congregation, console, consonant, construct, converge, etc.

It has the same meaning as "co-", which means:

together; mutually; jointly

"Conterminous" and "Coterminous" do mean the same.

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