coextension|kəʊɛkˈstɛnʃən| [f. co- 3 + extension.] Coincidence in extension. 1677Hale Prim.Orig.Man. i. i. 23 Some analogy, at least of co-extension, with my Body.1855H. Spencer Princ.Psychol. II. vi. v. 37 Coextension..or to speak..more comprehensibly—sameness in the quantity of space occupied.