Extent

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Middle English (in the sense ‘valuation of property, especially for taxation’): from Anglo-Norman French extente, from medieval Latin extenta, feminine past participle of Latin extendere ‘stretch out’ (see extend).

wiktionary

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From Middle English extente, from Anglo-Norman extente and Old French estente(“valuation of land, stretch of land”), from estendre, extendre(“extend”) (or from Latin extentus), from Latin extendere (See extend.)

etymonline

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extent (n.)

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.