The Collaborative International Dictionary of English v.0.48:

Coextend \Co`ex*tend\, v. t. [imp. & p. p. Coextended; p. pr.
   & vb. n. Coextending.]
   To extend through the same space or time with another; to
   extend to the same degree.
   [1913 Webster]

         According to which the least body may be coextended
         with the greatest.                       --Boyle.
   [1913 Webster]

         Has your English language one single word that is
         coextended through all these significations? --Bentley.
   [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

21 Moby Thesaurus words for "coextend":
   accompany, agree, be in phase, be in time, be parallel, coexist,
   coincide, concur, contemporize, equal, go alongside, go beside,
   isochronize, keep in step, keep pace with, match, parallel,
   run abreast, run parallel, synchronize, time