Definition
Two angles whose measures add together to equal 180 degrees. When placed side by side, they form a straight line.
Plain English
Two angles that, when added together, make a straight line. If one angle is 120 degrees, the other must be 60 degrees to be its supplementary angle.
Context Anchor
Seen in aviation math, chart work, and any discussion where angles or directions are being measured or compared.
Derivation
From the Latin supplementum, meaning 'something added to complete.' The second angle 'supplements' the first to complete a straight line of 180 degrees.
Why Pilots Care
Knowing this helps a pilot avoid angle mistakes when reading diagrams, working with headings, or following geometry in training material.
Analogy
If a straight line is the full 180 degrees, supplementary angles are two pieces that fit together to make that full straight line.
Intuition Check
Supplementary does not mean “extra” or “optional” here. It means the two angles add together to exactly 180 degrees.
Example Sentence 1
Since the wing's leading edge angle measured 110 degrees, its supplementary angle on the other side of the line was 70 degrees.
Example Sentence 2
During the navigation exercise the two course corrections formed supplementary angles that totaled a straight 180-degree reversal.