What does diametral mean?
Diametral is an adjective with both a precise geometric meaning and a vivid figurative one. Literally, it describes something relating to or lying along a diameter — a straight line passing through the center of a circle or sphere from one side to the other — and it appears frequently in technical fields such as engineering and mathematics, as in 'diametral pitch'. Figuratively, it signals total, uncompromising opposition: when two positions are described as being in diametral opposition, they occupy the most extreme possible distance from each other within a shared framework. This figurative use draws its power from the underlying geometry, since points at opposite ends of a diameter cannot be any farther apart. Diametral is a formal word, found mainly in academic, technical, and polished prose, and it is closely related to the more colloquial phrase 'diametrically opposed'.
Relating to, along, or in the direction of a diameter of a circle or sphere.
"The diametral section of the sphere passed exactly through its center."
Common in technical and mathematical writing.
(Figurative) Constituting complete or absolute opposition; directly contrary.
"The two witnesses gave diametral accounts of what had happened."
Usually appears in the phrases 'diametral opposition' or 'diametrically opposed'; formal register.
When two things are 'diametrally opposed', geometry is doing the arguing: they sit at opposite ends of the same diameter — as far apart as it's possible to get while still being connected.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of diametral
Diametral derives from the Latin 'diametralis', itself built on 'diameter', which traces back to Greek 'diametros' — from 'dia' ('through') and 'metron' ('measure'), literally a line that 'measures across' a circle. English adopted the word in late Middle English, initially in mathematical contexts, and later extended it figuratively to describe complete oppositeness. Its relatives include 'diameter' and the adverb 'diametrically', all sharing the same Greek root about measuring through or across.
Related word forms
How diametral is actually used
Formal register. The literal geometric sense ('diametral plane', 'diametral pitch' in engineering) is common in technical contexts, while the figurative sense usually appears in the fixed phrase 'diametral(ly) opposed/opposition'. In everyday speech, 'diametrically opposed' is far more frequent than 'diametral opposition'.
Easily confused with diametral
Diametric (as in 'diametrically opposed') is the more common adjective for figurative opposition, while diametral more often refers literally to a diameter or is used interchangeably in the sense of complete opposition.