Plural of epsilon: the fifth letter of the Greek alphabet (Ε, ε), or used to describe something very small in mathematics.
From Greek 'epsilon' (from 'e psilon' meaning 'simple e'), to distinguish it from 'ai'. The letter has been used in English since ancient times.
In mathematics, epsilon became the symbol for 'infinitely small'—mathematicians literally made invisible quantities invisible by naming them after a letter that looks like it's disappearing.
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