protractor
pruh-TRAK-ter
/prəˈtræktər/
A semicircular instrument for measuring and drawing angles.
Specifically for geometric measurement of angles, typically made of clear plastic or metal.
The story behind the word. The word 'protractor' comes from the Latin prefix 'pro-' meaning 'forward' and the verb 'trahere,' meaning 'to draw or pull.' In its original sense, to 'protract' meant to draw out or delineate. Thus, a protractor is an instrument that helps you 'draw forth' or measure angles and lines. It's a tool for extending and defining geometric shapes with precision.
Word relationships
- angle measurer: A descriptive, less formal term.
Commonly confused with
- compass: A compass is used to draw circles; a protractor is used to measure and draw angles.
Word family
- protract (verb): to prolong or extend in time; (archaic) to draw out or delineate
Collocations
- plastic protractor
- measure with a protractor
- draw an angle
- geometry set
Example sentences
- "Using her protractor, the student carefully measured the interior angles of the triangle." A student works on a geometry assignment.
- "Architects and engineers often use a protractor to ensure precision in their designs." Describing a drafting tool.
Memory hook
A 'protractor' helps you 'pro'ceed to 'tract' (draw) angles. Draw angles forward
When not to use
Don't confuse with a ruler (for measuring length) or a compass (for drawing circles).
Fun facts
- The earliest known protractors date back to ancient Greece, used by astronomers and navigators.
- Marine protractors are used on nautical charts for plotting courses.
- Some protractors are full circles (360 degrees) rather than the common semicircular (180 degrees) type.
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