Extension

google

ref

late Middle English: from late Latin extensio(n- ), from extendere ‘stretch out’ (see extend).

wiktionary

ref

From Middle English extensioun, from Old French estension, from Latin extensiō, extensiōnem.

etymonline

ref

extension (n.)

c. 1400, "swelling, bulging," from Latin extensionem/extentionem (nominative extensio/extentio) "a stretching out, extension," noun of action from past-participle stem of extendere (see extend). In a concrete sense, "extended portion of something" (a railroad, etc.), from 1852. Telephone sense is from 1906.