The Collaborative International Dictionary of English v.0.48:

Conterminous \Con*ter"mi*nous\, a. [L. conterminus. Cf.
   Conterminous.]
   Having the same bounds, or limits; bordering upon;
   contiguous.
   [1913 Webster]

         This conformed so many of them as were conterminous to
         the colonies and garrisons, to the Roman laws. --Sir M.
                                                  Hale.
   [1913 Webster] Conterranean

WordNet (r) 3.0 (2006):

conterminous
    adj 1: connecting without a break; within a common boundary;
           "the 48 conterminous states"; "the contiguous 48 states"
           [syn: conterminous, contiguous]
    2: having a common boundary or edge; abutting; touching; "Rhode
       Island has two bordering states; Massachusetts and
       Conncecticut"; "the side of Germany conterminous with
       France"; "Utah and the contiguous state of Idaho";
       "neighboring cities" [syn: adjacent, conterminous,
       contiguous, neighboring(a)]
    3: being of equal extent or scope or duration [syn:
       coextensive, coterminous, conterminous]

Moby Thesaurus II by Grady Ward, 1.0:

47 Moby Thesaurus words for "conterminous":
   accompanying, adjacent, adjoining, agreeing, bordering, buck,
   coetaneous, coeternal, coeval, coexistent, coexisting,
   coinstantaneous, collateral, combat, concomitant, concurrent,
   connecting, contemporaneous, contemporary, contend, contiguous,
   coterminous, dispute, duel, end to end, endeavor, endways, endwise,
   face to face, fight, immediate, isochronal, isochronous, joined,
   juxtaposed, neighbor, neighboring, next, oppose, repel, rival,
   simultaneous, traverse, unison, unisonous, vie, withstand