What is "coextend"

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.

According to which the least body may be coextended with the greatest.
--Boyle.

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

vb. (context ambitransitive English) To extend along with another.