An archaic or variant spelling of equinox, the twice-yearly moment when day and night are approximately equal length.
From Latin 'aequinoctium' (equal night), where 'aequus' means equal and 'nox' means night. The 'ee' prefix is an archaic variant spelling common in Middle English.
This word shows how English spelling was chaotic before standardization—the same concept appeared as equinox, aequinox, and eequinoctium depending on when and where it was written!
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