The Collaborative International Dictionary
Complementary angles
Complementary \Com`ple*men"ta*ry\, a. Serving to fill out or to complete; as, complementary numbers.
Complementary colors. See under Color.
Complementary angles (Math.), two angles whose sum is 90[deg].
Wiktionary
complementary angles
n. (context geometry English) A pair of angles that sum to a right angle.
WordNet
complementary angles
n. two angles whose sum is a right angle