hemisphere

noun

hemi·​sphere ˈhe-mə-ˌsfir 

plural hemispheres

1

a

: a half of the celestial sphere as divided into two halves by the horizon (see horizon sense 1b), the celestial equator, or the ecliptic

b

: half of a spherical or roughly spherical body (such as a planet)

specifically : the northern or southern half of the earth as divided by the equator (see equator sense 2) or the eastern or western half as divided by a meridian (see meridian sense 1a(2))

affected by the weather in the other hemisphere

c

: the inhabitants of a hemisphere of the Earth

2

: an area of knowledge or activity : sphere, province

a hemisphere of life heretofore unknown to us

3

: one of two half spheres (see sphere entry 1 sense 2a) formed by a plane (see plane entry 1 sense 2a) through the sphere's center : half of a round object

4

: a map or projection of a celestial hemisphere (see hemisphere sense 1a) or a terrestrial hemisphere (see hemisphere sense 1b)

5

: cerebral hemisphere

an injury to the left hemisphere

Did you know?

Hemisphere includes the prefix hemi-, meaning "half". The northern and southern hemispheres are divided by the equator, the circle halfway between Earth's two poles. The eastern and western hemispheres aren't divided so exactly, since there are no poles in the Earth's east-west dimension. Often the dividing line is said to be the "prime meridian"—the imaginary north-south line that runs through Greenwich, England, from which all longitude is calculated (itself being the 0° meridian). But for simplicity's sake, the eastern hemisphere is often said to include all of Europe, Africa, Australia, and Asia, while the western hemisphere contains North and South America and a great deal of ocean.

Examples of hemisphere in a Sentence

a tumor in the right cerebral hemisphere

Recent Examples on the Web

Rather than the neo-isolationist that he’s often accused of being, Trump is talking like a neo-imperialist, at least in our own hemisphere. —Rich Lowry, National Review, 10 Jan. 2025

Canada and the United States share the longest border between any two countries on the planet, its economies and cultures are deeply enmeshed, and the relationship between Washington and Ottawa is one of the most durable in the hemisphere. —Philip Elliott, TIME, 7 Jan. 2025

Advertisement One of the problems is that the right hemisphere doesn’t track time. —Sandy Cohen, Los Angeles Times, 7 Jan. 2025

The Karoo is largely free of light pollution and offers spectacular views of the southern celestial hemisphere. —Biénne Huisman, Travel + Leisure, 15 Dec. 2024

Word History

Etymology

Middle English hemispere, from Latin hemisphaerium, from Greek hēmisphairion, from hēmi- + sphairion, diminutive of sphaira sphere

First Known Use

14th century, in the meaning defined at sense 1a

Phrases Containing hemisphere

• cerebral hemisphere
• eastern hemisphere
• northern hemisphere
• southern hemisphere
• western hemisphere

Kids Definition

hemisphere

noun

hemi·​sphere ˈhem-ə-ˌsfi(ə)r 

1

: one of the halves of the earth as divided by the equator or by a meridian

2

: one of two halves of a sphere

3

: cerebral hemisphere

Medical Definition

hemisphere

noun

hemi·​sphere -ˌsfi(ə)r 

: half of a spherical structure or organ: as

a

: cerebral hemisphere

b

: either of the two lobes of the cerebellum of which one projects laterally and posteriorly from each side of the vermis