planar

Etymology

The OED, in its 2006 revision, treats it as formed from English plane + -ar, on the model of linear,^[2][3] and compares the Late Latin adjective, recorded in the 5th century.^[2] Most other dictionaries derive it directly from that adjective: it is borrowed from Late Latin plānāris (“flat, level, on level ground”),^[4][5][6][7] from plānum (“flat surface”)^[8][9] or plānus (“flat, even, level”),^[4][5][6] with the suffix -āris.^[8][7] Etymonline traces the Latin word to Proto-Indo-European *pele- (“flat; to spread”),^[9] and the American Heritage Dictionary to *pelə-.^[4] It is related to plane and plain.^[4][6]

Earliest recorded meaning

Of or relating to a plane; lying in a plane, flat: 1850, in the mathematical papers of A. Cayley.^[2][8][9] Dictionary.com dates it to 1840–50.^[7]

Semantic evolution

Etymonline notes that an earlier adjective of the same meaning, planary, was used from the 1660s.^[9] In the 20th century electronics took it up, first for a thermionic valve with plane-parallel electrodes (1937), then for solid-state devices whose regions of different conductivity type have their boundaries in a single plane, and for the process that makes them (1965).^[2][3] It is also used of a flat, two-dimensional quality in pictures and design.^[8][4]

Timeline

• 1850 – of or relating to a plane; lying in a plane, flat.^[2][8][9]
• 1937 – electronics, of a valve with plane-parallel electrodes.^[2]
• 1965 – electronics, of a solid-state device with its junctions in one plane.^[2][3]

Meanings

Adjective

1. Of, relating to or lying in a plane; two-dimensional: The four points are planar, so they fit on one sheet.^[4][8][5][2]
2. Flat; having a flat surface or a flat, two-dimensional quality: a painting built from planar shapes.^[4][8]
3. (electronics) Of a semiconductor device, having the boundaries of its n-type and p-type regions in one plane; of the process used to make such devices.^[2][3]

Word family

• planarity
• uniplanar

Related words

• plane
• planate
• plain
• linear
• coplanar

References

1. ^ a b Wiktionary, the free dictionary, https://en.wiktionary.org
2. ^ a b c d e f g h i Oxford English Dictionary Online (accessed March 2026), Oxford: Oxford University Press
3. ^ 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
4. ^ a b c d e f g The American Heritage Dictionary of the English Language (online 2024), 5th ed., Boston: Houghton Mifflin Harcourt
5. ^ a b c Collins English Dictionary (2023), Glasgow: HarperCollins
6. ^ a b c Klein, Ernest. A Comprehensive Etymological Dictionary of the English Language. 2 vols. Amsterdam: Elsevier, 1966–1967.
7. ^ a b c Dictionary.com Unabridged (2016), based on the Random House Unabridged Dictionary, New York: Random House
8. ^ a b c d e f g Merriam-Webster Unabridged Dictionary (2024), online ed., Springfield, Mass.: Merriam-Webster
9. ^ a b c d e Harper, Douglas. Online Etymology Dictionary, https://www.etymonline.com