hemi·​sphere ˈhe-mə-ˌsfir How to pronounce hemisphere (audio)
plural hemispheres
: a half of the celestial sphere as divided into two halves by the horizon (see horizon sense 1b), the celestial equator, or the ecliptic
: 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
: the inhabitants of a hemisphere of the Earth
: an area of knowledge or activity : sphere, province
a hemisphere of life heretofore unknown to us
: 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
: a map or projection of a celestial hemisphere (see hemisphere sense 1a) or a terrestrial hemisphere (see hemisphere sense 1b)
: 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 In particular, the right hemisphere of the infant’s brain undergoes neurological development that leads to the ability to relate to others. Emilie Le Beau Lucchesi, Discover Magazine, 9 Nov. 2023 Six cyclones are spinning through the tropics right now, churning over the ocean and sometimes over land in both hemispheres. Matthew Cappucci, Washington Post, 24 Oct. 2023 Every year, vaccine makers in each hemisphere build a new formula based on whatever is circulating. Maryn McKenna, WIRED, 10 Nov. 2023 At the same time,activists insist that nations throughout the hemisphere must tackle the growing migration phenomenon, including the role of civil society, private companies and international cooperation. Soudi Jiménez, Los Angeles Times, 27 Oct. 2023 Even if some of the returns envisioned by China’s newest partners in the hemisphere have not yet materialized, officials at both the Pentagon and the State Department have spent years worrying that China’s string of diplomatic victories has laid the groundwork for future threats. Karen Deyoung, Washington Post, 2 Oct. 2023 In 2015 Emory neurosurgeons implanted the first of the new devices by threading one electrode into area 25 in each hemisphere and connecting these to a pacemaker. Ingrid Wickelgren, Scientific American, 20 Sep. 2023 If migrating birds lose their winter refuges, the consequences will ripple across the hemisphere. Emily Anthes, New York Times, 29 Aug. 2023 The eighties were turbulent times in the lower hemisphere, to put it mildly. Cressida Leyshon, The New Yorker, 30 Oct. 2023 See More

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'hemisphere.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.

Word History


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

Time Traveler
The first known use of hemisphere was in the 14th century

Dictionary Entries Near hemisphere

Cite this Entry

“Hemisphere.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/hemisphere. Accessed 8 Dec. 2023.

Kids Definition


hemi·​sphere ˈhem-ə-ˌsfi(ə)r How to pronounce hemisphere (audio)
: one of the halves of the earth as divided by the equator or by a meridian
: one of two halves of a sphere

Medical Definition


hemi·​sphere -ˌsfi(ə)r How to pronounce hemisphere (audio)
: half of a spherical structure or organ: as
: either of the two lobes of the cerebellum of which one projects laterally and posteriorly from each side of the vermis
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