triangular

Etymology

It is borrowed from Late Latin triangulāris (“triangular, pertaining to a triangle”),^{[2][3][4][5][6]} from Latin triangulum (“triangle”) and the adjective suffix -āris,^[6][7][8] which in English is -ar.^[2][4] Klein notes that triangulāris occurs only once in Classical Latin, where the usual adjective was triangulus (“three-cornered”).^[8][3] The noun triangulum is the neuter of that adjective, formed from tri- (“three”) and angulus (“corner, angle”).^[3] The OED compares Old French triangulier, recorded in the 13th century.^[2]

Earliest recorded meaning

Having the form of a triangle, three-sided or three-cornered: about 1541, in Robert Copland's translation of Guy de Chauliac's Questyonary of Cyrurgyens.^[2][9] Etymonline dates the word to about 1400,^[3] Merriam-Webster to the 14th century,^[6] and the Shorter Oxford and the Oxford Dictionary of English to the mid 16th century.^[4][5]

Semantic evolution

The geometrical sense widened in the 17th century to things set at the three corners of a triangle (1622, in Drayton's Poly-Olbion) and to solids with three edges, such as a prism (1644, in Digby).^[2][9] From 1701 the word also meant "relating to a triangle", as in triangular compasses, with three legs for copying triangles.^[2][3] From 1706 it also named the triangular numbers, 1, 3, 6, 10 and so on, got by adding up the natural numbers in turn.^[2][4] Johnson (1755) defined it simply as "having three angles", quoting Spenser.^[10] The figurative sense, involving three persons or parties, appears in 1812, in Thomas Jefferson's writings;^[2][3] the Shorter Oxford illustrates it with Hardy's "triangular situation" of a man, his wife and another woman, and also records the triangular trade, in which a country pays for imports from one country with exports to another.^[4]

Timeline

• c. 1400 – first use according to Etymonline.^[3]
• c. 1541 – shaped like a triangle; three-sided, three-cornered.^[2]
• 1622 – placed at the corners of a triangle (now obsolete).^[2][9]
• 1644 – having three edges, as a prism.^[2][9]
• 1701 – relating to a triangle.^[2][3]
• 1706 – triangular number.^[2]
• 1812 – figurative, involving three persons or parties.^[2][3]
• 1816 – of a solid, having triangles as its faces (rare).^[2][4]

Meanings

Adjective

1. Shaped like a triangle; having three sides and three corners: a triangular patch of lawn between the roads.^[11][6][2]
2. Having a triangle as its base or cross-section; three-edged, as a prism or pyramid.^[11][6][4]
3. Of or relating to a triangle or to the construction of triangles.^[11][2][4]
4. Involving three persons, parties or parts: triangular talks between the two companies and the union.^[11][2][4]
5. triangular number: any of the numbers 1, 3, 6, 10, 15 and so on, obtained by adding the natural numbers in turn.^[4][2]
6. triangular trade: a system of trade in which a country pays for its imports from one country by its exports to another.^[4]

Word family

• triangularity
• triangularly
• subtriangular
• triangular number
• triangular trade
• triangular matrix

Related words

• triangle
• angle
• angular
• triangulate

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 Oxford English Dictionary Online (accessed March 2026), Oxford: Oxford University Press
3. ^ a b c d e f g h i Harper, Douglas. Online Etymology Dictionary, https://www.etymonline.com
4. ^ a b c d e f g h i j k Shorter Oxford English Dictionary on Historical Principles (2002), 5th ed., ed. William R. Trumble and Angus Stevenson, Oxford: Oxford University Press
5. ^ a b Stevenson, Angus, ed. (2010), Oxford Dictionary of English, 3rd ed., Oxford: Oxford University Press
6. ^ a b c d e Merriam-Webster Unabridged Dictionary (2024), online ed., Springfield, Mass.: Merriam-Webster
7. ^ Dictionary.com Unabridged (2016), based on the Random House Unabridged Dictionary, New York: Random House
8. ^ a b Klein, Ernest. A Comprehensive Etymological Dictionary of the English Language. 2 vols. Amsterdam: Elsevier, 1966–1967.
9. ^ a b c d Kay, Christian; Roberts, Jane; Samuels, Michael; Wotherspoon, Irené, eds. (2009), Historical Thesaurus of the Oxford English Dictionary, Oxford: Oxford University Press; online edition (2024)
10. ^ Johnson, Samuel (1755), A Dictionary of the English Language, London; 4th ed. 1773; Johnson's Dictionary Online, ed. Beth Rapp Young et al.
11. ^ a b c d Collins English Dictionary (2023), Glasgow: HarperCollins