either of two angles that added together produce an angle of 180°.
“Compliment” vs. “Complement”: How To Pick The Right WordCompliment and complement are commonly confused terms because they're pronounced alike and originally shared some meanings ...
Compare complementary angle.
Origin of supplementary angle
First recorded in 1830–40
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
British Dictionary definitions for supplementary angle
either of two angles whose sum is 180°Compare complementary angle
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012