Definition of triangle
1 : a polygon having three sides — compare spherical triangle
2a : a percussion instrument consisting of a rod of steel bent into the form of a triangle open at one angle and sounded by striking with a small metal rodb : a drafting instrument consisting of a thin flat rightangled triangle of wood or plastic with acute angles of 45 degrees or of 30 degrees and 60 degrees
3 : a situation in which one member of a couple is involved in a love affair with a third person
Examples of triangle in a sentence
She cut the sandwiches into triangles.
Origin and Etymology of triangle
Middle English, from AngloFrench, from Latin triangulum, from neuter of triangulus triangular, from tri + angulus angle
First Known Use: 14th century
TRIANGLE Defined for English Language Learners
triangle
playDefinition of triangle for English Language Learners

: a shape that is made up of three lines and three angles

: something that is shaped like a triangle

: a musical instrument that is made of a steel rod bent into the shape of a triangle and that you play by hitting with a metal rod
TRIANGLE Defined for Kids
triangle
playDefinition of triangle for Students
1 : a flat geometric figure that has three sides and three angles
2 : something that has three sides and three angles <a triangle of land>
3 : a musical instrument made of a steel rod bent in the shape of a triangle with one open angle
Medical Dictionary
triangle
playMedical Definition of triangle
: a threesided region or space and especially an anatomical one—see anterior triangle, carotid triangle, femoral triangle, posterior triangle, suboccipital triangle
Learn More about triangle

See words that rhyme with triangle Spanish Central: Translation of triangle Nglish: Translation of triangle for Spanish speakers Britannica English: Translation of triangle for Arabic speakers Britannica.com: Encyclopedia article about triangle
Seen and Heard
What made you want to look up triangle? Please tell us where you read or heard it (including the quote, if possible).
Writing? Check your grammar now!