Etymology Map
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Equator

2 stages from Medieval Latin to English.

Today it means an imaginary line around the Earth's middle

Where does the word "equator" come from? It comes from Medieval Latin aequator, adopted directly into English (1300s).

1
Stage 1 of 2
aequator
Medieval Latin · medieval
"equalizer"
Medieval Latin 'circulus aequator diei et noctis', the circle equalizing day and night
2
Stage 2 of 2
equator
English · 1300s
"celestial equator"
geographers applied it to the Earth
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Read the full story

Equator’s story begins in Medieval Latin: aequator meant “equalizer.” Medieval Latin 'circulus aequator diei et noctis', the circle equalizing day and night. It reached English by 1300s as equator. Geographers applied it to the Earth. Today, equator means an imaginary line around the Earth's middle.