- (sciences) emittance, extinction coefficient. (Can we add an example for this sense?)
- (mathematics) A small number, usually in company of δ.
- For each ε > 0, there exists a δ > 0, ...
- (mathematics, computer science) empty string
- Lower case epsilon, the fifth letter of the ancient and modern Greek alphabets. Its name was εἶ, later ἒ ψιλόν, and presently έψιλον. It represents roughly the same sound in both alphabets: in Modern Greek, a somewhat lowered variant of the mid front unrounded vowel: /e/ or /e̞/. It is preceded by δ and followed by ϝ.