What does spheroid mean?
A spheroid is a three-dimensional form that is close to, but not necessarily exactly, a sphere. More precisely, in geometry it is an ellipsoid formed by rotating an ellipse around one axis, so it has a circular equator and a pair of unequal polar and equatorial axes. A flattened spheroid is called oblate, while a spheroid elongated at the poles is called prolate. Earth is commonly described as an oblate spheroid because its rotation causes it to bulge slightly around the equator and flatten at the poles. Outside technical geometry, the word can refer more broadly to an object or body with a rounded, sphere-like form. It is useful when precision matters: “sphere” suggests perfect roundness, whereas “spheroid” allows for a measured distortion from that shape.
A geometric solid whose surface is generated by rotating an ellipse around one of its axes, with two equal semi-axes; it resembles a sphere but may be flattened or elongated.
"The observatory used a precise spheroid to represent the planet's shape."
The word is chiefly used in geometry, astronomy, and technical description.
An object or body with a rounded form resembling a sphere.
"The artist polished the river stone into a smooth spheroid."
This is a general, nontechnical use.
The plural is spheroids, with no additional ending.
"The model contains several smooth spheroids representing small celestial bodies."
Earth is not a perfect sphere but an oblate spheroid—slightly flattened at the poles by its rotation.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does spheroid come from?
The word comes from Greek sphaira, meaning “ball” or “sphere,” combined with the suffix -oeidēs, meaning “resembling” or “like.” It entered English through Latin and French in the 17th century in the sense of a geometrical solid resembling a sphere. The same Greek root underlies sphere, spherical, and several other terms connected with rounded forms.
Related word forms
How spheroid is actually used
In geometry, a spheroid is a specific kind of ellipsoid with two equal axes. In general description, it is often used for a slightly distorted spherical object.
Easily confused with spheroid
A sphere is perfectly round, while a spheroid is a sphere-like ellipsoid whose polar and equatorial axes differ.