/ɪˈkweɪʒən/
[noun] A mathematical statement showing that two things are equal, often written with an equals sign between them. It can also mean the act of treating two things as being the same or equally important.
Before mathematicians claimed it, 'equation' simply meant the act of making things equal — like balancing a set of scales.
The word 'equation' travels to us from the Latin verb aequare, meaning 'to make equal' or 'to level', which itself grew from the adjective aequus, meaning 'level', 'flat', or 'equal'. This root aequus was deeply embedded in Roman thought — it carried ideas not just of mathematical sameness, but of fairness, calm, and balance. From aequare, Latin formed the noun aequatio, meaning 'the act of making equal' or 'an equalization'. It was this noun, aequatio, that slowly made its way into the European intellectual tradition.
During the medieval period, scholars writing in Latin across Europe used aequatio in philosophical and astronomical texts. When Chaucer's contemporary and the broader scholarly community began translating scientific Arabic and Greek works into Latin, the word gained momentum. Medieval astronomers spoke of the 'equation of time' — the correction needed to align the movement of the sun with a perfect clock — and this is one of the earliest specialized uses of the concept behind the word, centuries before algebra made it famous.
The word entered English in the late 14th century, borrowed directly from Latin aequatio. At first, its meaning was broad and general — simply the act of making two things equal, or the state of being balanced. It appeared in texts about astronomy and philosophy before mathematics fully claimed it. The strictly algebraic sense, referring to a formal statement that two expressions are equal, developed gradually as symbolic mathematics grew more sophisticated in the 15th and 16th centuries.
The Latin root aequus proved extraordinarily productive in English, giving the language a whole family of related words through different paths. Latin aequus → Old French equal → English 'equal'; Latin aequitas → Old French equite → English 'equity'; Latin aequare → Medieval Latin aequilibrium → English 'equilibrium'; and Latin aequinoctium (from aequus + nox, meaning 'night') → Old French equinoxe → English 'equinox', the moment when day and night are perfectly balanced. Each of these words carries that same ancient sense of levelness and fairness.
What makes 'equation' particularly interesting is how it straddles two worlds — the emotional and the mathematical. In everyday language, we still use it in its older, more human sense: 'money is not part of my equation', or 'we have to consider the human equation'. These uses echo the original Roman meaning of balance and consideration, reminding us that long before algebra existed, the idea of making things equal was bound up with justice, fairness, and the careful weighing of life's competing demands. The equals sign itself, '=', was only invented by Welsh mathematician Robert Recorde in 1557, centuries after the word equation was already in use — proof that the concept outran its famous symbol.