Etymology
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invaluable (adj.)
1570s, "above value, too valuable for exact estimate," from in- (1) "not" + value (v.) "estimate the worth of" + -able. It also has been used in a sense "without value, worthless" (1630s, from in- + valuable). Related: Invaluably.
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priceless (adj.)

"having a value beyond price, invaluable," 1590s, from price (n.) + -less. Compare worthless, which has the opposite sense. Colloquial sense of "delightful, amusing" is attested from 1907. Related: Pricelessly; pricelessness.

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inestimable (adj.)
late 14c., "beyond estimation or measure, not to be computed," from Old French inestimable "priceless" (14c.) or directly from Latin inaestimabilis "invaluable, incalculable," also "not estimable, valueless," from in- "not, opposite of" (see in- (1)) + aestimabilis "valuable, estimable," from aestimare (see esteem (v.)). Meaning "too precious to set a value on, priceless" is attested by 1570s. Related: Inestimably; inestimability.
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koine (n.)

common literary dialect of Greek in the Roman and early medieval period, 1903, from feminine singular of Greek koinos "common, ordinary" (see coeno-). Used earlier as a Greek word in English. From 1926 of other dialects in similar general use.

[Isocrates] helped to lay the foundations for that invaluable vehicle of civilization, the Koinê Dialektos, through which, at the price of becoming easy, flat, common, and a little soulless, the Greek language in the Hellenistic period evangelized the whole Mediterranean world. [Gilbert Murray, "Greek Studies," 1946]
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