What does semicircle mean?
A semicircle is one half of a circle, bounded by a curved arc and a straight line. The term is used most often in geometry, but it also describes objects, spaces, and arrangements with a half-circle shape: a doorway may have a semicircular top, for example, while a class might sit in a semicircle around a teacher. When applied to people, especially performers or audience members, it emphasizes a curved formation in which everyone can face a common centre. A semicircle should not be confused with a hemisphere, which is three-dimensional and represents half a sphere rather than half a circular plane. In general use, the word is precise and formal, with no strong positive or negative connotation outside specialised contexts.
A two-dimensional figure or shape consisting of half a circle, bounded by an arc and a diameter; by extension, a half-circle-shaped object or area.
"The diagram shows a semicircle divided into two equal quadrants."
In technical geometry, the straight boundary is the diameter of the original circle.
An arrangement of people, especially performers or audience members, in a curved half-circle.
"The panel formed a semicircle in the centre of the stage."
The regular plural is used for both geometric figures and semicircular arrangements or objects.
"The pupils drew semicircles and label their diameters."
A semicircle is what you get when a circle makes a simple, geometric cut in half.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does semicircle come from?
The word was formed in the early 19th century from the prefix semi-, meaning 'half', and circle, which comes from Latin circulus, a diminutive of Latin circum, meaning 'around'. The geometric sense developed alongside the broader meaning of any semicircular form or arrangement. Its second element belongs to the same Latin family as circular, circumference, and circuit.
Related word forms
How semicircle is actually used
In geometry, the term normally refers to the two-dimensional figure. Its use for people or seating is common in descriptions of arrangements, though it can sound more formal than 'in a half-circle'.
Easily confused with semicircle
A semicircle is a two-dimensional half-circle or half-disc, whereas a hemisphere is the three-dimensional half of a sphere.