- trigonometry (n.)
- "branch of mathematics that deals with relations between sides and angles of triangles," 1610s, from Modern Latin trigonometria (Barthelemi Pitiscus, 1595), from Greek trigonon "triangle" (from tri- "three" (see tri-) + gonia "angle" (see -gon)) + metron "a measure" (see meter (n.2)).
