diameter
n.-
1 distance across a circle (n.) B1 Intermediate Maththe length of a straight line that goes from one side of a circle to the other, passing through the center.
the length of a straight line segment passing through the center of a figure, especially a circle or sphere, and terminating at the periphery.
ExampleThe pipe has a diameter of ten centimeters, so it should fit perfectly.
ExampleTo calculate the circumference accurately, the engineer first measured the inner diameter of the cylinder using a digital caliper.
PitfallThe diameter from the circle is ten centimeters.The diameter of the circle is ten centimeters.Use the preposition 'of' to link the measurement to the object being measured.
-
2 the line itself (n.) B2 Upper Intermediate Matha straight line that divides a circle into two equal halves by passing through the middle.
a chord that passes through the center of a circle or sphere.
ExampleDraw a diameter across the circle to show where to cut the paper.
ExampleThe geometry problem required students to construct a diameter that was perpendicular to the given chord.
- axis
- centerline
-
3 maximum distance in a space (n.) C2 Proficiency Technical Maththe largest possible distance between any two points in a specific area or shape.
the maximum distance between any two points in a metric space or the maximum eccentricity over all vertices in a graph.
ExampleThe diameter of this network is small, meaning any two points are closely connected.
ExampleIn graph theory, the diameter of a graph is defined as the greatest distance between any pair of vertices.
UsageUsed primarily in advanced mathematics, topology, and graph theory.
- maximum width
From Old French diametre (French diamètre), from Latin diametros, from Ancient Greek διάμετρος (diámetros) (γραμμή (grammḗ)) (diametros grammē, “line measuring across”), from διά (diá, “across”) + μέτρον (métron, “measure”). By surface analysis, dia- + -meter.
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.
Last updated June 19, 2026