What does concave mean?
"Concave" is an adjective describing a surface or outline that curves inward, forming a hollow — like the inside of a bowl, a spoon's scooped bowl, or a crater's depression. It is most at home in technical fields: optics distinguishes concave mirrors and lenses, which spread light rays apart, from convex ones, which bring them together; geometry uses it for polygons and functions that curve inward; anatomy applies it to features such as a concave chest. The word derives from Latin "concavus," meaning hollowed out, sharing its root "cavus" (hollow) with words like "cavity" and "cavern." Its natural opposite is "convex," which curves outward, and the pair is often taught together because confusing them is easy. A useful mnemonic: think of a cave — something you step inside — to remember which way a concave surface bends. Though somewhat formal in tone, "concave" is precise, widely understood, and indispensable whenever exactness about curvature matters.
Curving inward like the interior of a circle or sphere; having a hollowed surface.
"The concave slope funneled rainwater toward the center of the basin."
Standard pronunciation stresses the first syllable (/ˈkɒn.keɪv/); some speakers also use /kɒnˈkeɪv/.
A concave lens or mirror; a surface or object that is concave.
"The optician prescribed concaves to correct his myopia."
Chiefly used in optics; less common than the adjectival form.
To make concave, or to become concave; to hollow out.
"Years of erosion had concaved the riverbank into a smooth shelf."
Rare and chiefly technical; the noun form of this verb is "concavation."
Applies only when "concave" is used as a noun (chiefly in optics, meaning concave lenses or mirrors). As an adjective it does not inflect for number.
"The laboratory kept a set of ground-glass concaves for the demonstration."
A handy memory trick: a cave is a hollow you enter — and 'concave' shares that same Latin root for hollow, so it's literally shaped like a cave.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of concave
English borrowed "concave" directly from Latin "concavus" ("hollowed out"), formed from "com-" (an intensifying prefix here) plus "cavus" ("hollow"). The word entered English in the late Middle English period, appearing by the fourteenth to fifteenth centuries, largely in scholarly and scientific writing. It shares its root "cavus" with "cavity," "cavern," "excavate," and "cove," all of which preserve the sense of hollowness.
Related word forms
How concave is actually used
Primarily a technical or descriptive term common in mathematics, physics, anatomy, and design; it sounds more formal than everyday words like 'hollow' or 'dented'. In British English the adjective is sometimes pronounced /kənˈkeɪv/ with reduced first-syllable stress; as a noun (a concave lens), the stress falls on the final syllable (/ˈkɒn.keɪv/ vs /kɒnˈkeɪv/) in careful usage.
Easily confused with concave
Convex describes a surface that curves outward toward the viewer, while concave curves inward away from the viewer.