What does equatorial mean?
Equatorial describes anything relating to, or lying near, the Earth's equator — the imaginary line encircling the planet midway between its poles. In everyday geography and science writing, the word most often characterizes the hot, humid climates found along this belt: an equatorial rainforest receives heavy rainfall year-round, and equatorial regions typically see little seasonal variation in temperature or day length. The term extends into astronomy, where it refers to the celestial equivalent of the equator and to equatorial mounts, which allow telescopes to follow the apparent rotation of the sky. Derived from the Latin aequator, meaning 'equalizer', the word carries a precise, technical connotation rather than an emotive one. It appears frequently in fixed phrases such as equatorial climate, equatorial forest, and the proper name Equatorial Guinea. For writers, it offers a concise way to evoke both a location on the globe and the lush, steaming conditions associated with it.
Relating to, situated near, or characteristic of the Earth's equator; in astronomy, relating to the celestial equator.
"The ship sailed through equatorial waters under an unbroken canopy of cloud."
Most often used attributively before a noun, as in 'equatorial climate' or 'equatorial forest'.
A telescope mounted so that it can be driven to follow the rotation of the sky about the celestial pole; short for 'equatorial telescope' or 'equatorial mount'.
"He set up his equatorial on the lawn and spent the evening tracking Saturn."
A specialist usage confined mainly to amateur astronomy; the adjective sense is far more common today.
Applies only to the rare astronomical noun; the adjective does not inflect.
"Older observatories often kept several large equatorials for long-exposure photography."
The line that gives 'equatorial' its name comes straight from Latin aequator, 'the equalizer' — the one place on Earth where day and night are always evenly matched.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of equatorial
Equatorial derives from the Latin aequator, literally 'the equalizer', formed from aequare ('to make equal') because day and night are roughly equal at the equator throughout the year. The English noun equator appeared first, in the late Middle Ages or early modern period, and the adjective equatorial followed in the early modern era as scientific geography developed. It shares its Latin root with related words such as equal, equation, and equilibrium, all built on the idea of balance or evenness.
How equatorial is actually used
Primarily formal, scientific, and geographical in register; common in geography, climatology, and astronomy writing. As a noun it survives mainly in astronomy for an equatorially mounted telescope.
Easily confused with equatorial
Equatorial relates to the equator, while equine relates to horses.