Earliest Known Uses of Some of the Words of Mathematics (O)
Oblique angle appears in English in 1695 in Geometry Epitomized by William Alingham: "An Oblique Angle, is either Acute or Obtuse" [OED].
OBTUSE TRIANGLE. Amblygonium and obtuse angled triangle appear in 1570 Billingsley’s translation of Euclid: "An ambligonium or an obtuse angled triangle" [OED].
In 1828 Webster’s dictionary has: "If one of the angles is obtuse, the triangle is called obtusangular or amblygonous."
Obtuse triangle is found in 1852 in The Lives of Winfield Scott and Andrew Jackson by Josh Tyler Headley: "Thus the American army stood like an obtuse triangle of which the British line formed the base." [Google print search]
OCTAGON. Octoagon is found in 1594 in A. I. Cameron, Warrender Papers (1932): “Table formed of thrie partis of octoagon.” [OED]
ODD FUNCTION is found in 1819 in New Series of The Mathematical Repository by Thomas Leybourn [Google print search].
