observable

Etymology

It is borrowed from Latin observābilis (“able to be observed, perceptible; that must be attended to; remarkable”),^[2][3][4][5] from observō (“to watch over, note, heed, comply with”) and the suffix -ābilis, English -able.^[2][3][4] Merriam-Webster gives French as the immediate source,^[6] and the OED compares Middle French observable, recorded from about 1508.^[2] The Latin verb is formed from ob (“in front of, before”) and servō (“to watch, keep safe”), from Proto-Indo-European *ser- (“to protect”).^[3]

Earliest recorded meaning

Able to be observed or noticed; perceptible: 1589, in Puttenham's Arte of English Poesie.^[2] Merriam-Webster also dates the word to 1589,^[6] while Etymonline dates it to about 1600 and this sense to the 1640s.^[3]

Semantic evolution

Beside "perceptible", the adjective had from the early 17th century the sense "that must be kept or followed", of customs and rules, which the OED records from 1608 to 1879,^[2][3][5] as well as, from 1609, "notable, remarkable", which weakened to "worth noticing", now rare.^[2][3] Johnson (1755) defined it as "remarkable; eminent; such as may deserve notice".^[7] As a noun it meant a noteworthy thing from 1639 to 1819,^[2] and in philosophy from 1660, in Henry More, a thing that can be perceived by the senses.^[2] In physics it became, from 1930 in Dirac's Principles of Quantum Mechanics, a quantity that can in principle be measured,^[2] and in astronomy the observable universe is recorded from 1932.^[2]

Timeline

• 1589 – perceptible, noticeable.^[2][6] Etymonline dates this sense to the 1640s.^[3]
• 1608 – that must be kept or followed (obsolete by 1879).^[2] Etymonline dates it to about 1600.^[3]
• 1609 – notable, remarkable; later, noteworthy.^[2]
• 1639 – noun, a noteworthy thing (obsolete by 1819).^[2]
• 1660 – noun, a thing perceptible by the senses.^[2]
• 1930 – noun, in physics, a measurable quantity.^[2]
• 1932 – observable universe.^[2]

Meanings

Adjective

1. Able to be seen, noticed or detected; perceptible: There was no observable change in his breathing.^[6][2][8]
2. Requiring to be kept or followed, as a custom or rite.^[6][5][2]
3. Worth noticing; noteworthy (now rare).^[2][6][5]

Noun

1. In physics, a quantity that can be measured, such as energy or momentum.^[2][6]
2. Something that can be perceived through the senses, directly or by means of instruments; a phenomenon.^[6][2]
3. (archaic) Something noteworthy or unusual.^[6][2]

Word family

• observably
• observability
• nonobservable
• unobservable

Related words

• observe
• observation
• observance
• observatory

References

1. ^ a b Wiktionary, the free dictionary, https://en.wiktionary.org
2. ^ a b c d e f g h i j k l m n o p q r s t u v w Oxford English Dictionary Online (accessed March 2026), Oxford: Oxford University Press
3. ^ a b c d e f g h Harper, Douglas. Online Etymology Dictionary, https://www.etymonline.com
4. ^ a b Klein, Ernest. A Comprehensive Etymological Dictionary of the English Language. 2 vols. Amsterdam: Elsevier, 1966–1967.
5. ^ a b c d Shorter Oxford English Dictionary on Historical Principles (2002), 5th ed., ed. William R. Trumble and Angus Stevenson, Oxford: Oxford University Press
6. ^ a b c d e f g h i Merriam-Webster Unabridged Dictionary (2024), online ed., Springfield, Mass.: Merriam-Webster
7. ^ Johnson, Samuel (1755), A Dictionary of the English Language, London; 4th ed. 1773; Johnson's Dictionary Online, ed. Beth Rapp Young et al.
8. ^ Collins English Dictionary (2023), Glasgow: HarperCollins