"one who or that which extends or stretches," 1610s, agent noun from extend (v.). Middle English had extendour "surveyor, assessor."

"capable of being extended," 1610s, from French extensible, from stem of Latin extendere "to spread out" (see extend). Earlier was extendible (late 15c.).

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.

"vast, far-reaching;" c. 1600 of immaterial, c. 1700 of material things; from Late Latin extensivus, from extens-, past-participle stem of Latin extendere "to stretch out, spread" (see extend). Earlier in a medical sense, "characterized by swelling" (early 15c.). Related: Extensively; extensiveness.

c. 1300, extente, "tax levied on value; value of property for taxation," from Anglo-French extente, estente "extent, extension;" in law, "valuation of land, stretch of land," from fem. past participle of Old French extendre "extend," from Latin extendere "to spread out, spread" (see extend). Meaning "degree to which something extends" is from 1590s.

1530s, "make thin, lean, slender, or rare; reduce in thickness or density" (the literal sense, now rare); from Latin extenuatus, past participle of extenuare "lessen, make small, reduce, diminish, detract from," from ex "out" (see ex-) + tenuare "make thin," from tenuis "thin," from PIE root *ten- "to stretch." Used over the years in a variety of literal and figurative senses in English. From 1560s as "to lessen, make smaller in degree or appearance, make less blamable, lower in importance or degree." Related: Extenuated; extenuating. Extenuating circumstances (1660s) are those which lessen the magnitude of guilt (opposed to aggravating).

early 15c., extenuacioun, "action or process of making or becoming thin," from Latin extenuationem (nominative extenuatio) "a lessening, diminution," noun of action from past-participle stem of extenuare "lessen, reduce, diminish," from ex "out" (see ex-) + tenuare "make thin," from tenuis "thin," from PIE root *ten- "to stretch." From 1610s as "act of making less in importance or degree, a diminishing (as of blame or guilt) in fact or estimation, mitigation."

"situated or being outside, pertaining to or connected with that which is outside," 1520s, from Latin exterior "outward, outer, exterior," comparative of exterus "on the outside, outward, outer, of another country, foreign," itself a comparative of ex "out of" (see ex-). As a noun, "outer surface or aspect" from 1590s.

1540s, "drive away," from Latin exterminatus, past participle of exterminare "drive out, expel, put aside, drive beyond boundaries," also, in Late Latin "destroy," from phrase ex termine "beyond the boundary," from ex "out of" (see ex-) + termine, ablative of termen "boundary, limit, end" (see terminus).

Meaning "destroy utterly" is from 1640s in English, a sense found in equivalent words in French and in the Vulgate; earlier in this sense was extermine (mid-15c.). Related: Exterminated; exterminating.