omicron

Greek alphabet
Αα Alpha	Νν Nu
Ββ Beta	Ξξ Xi
Γγ Gamma	Οο Omicron
Δδ Delta	Ππ Pi
Εε Epsilon	Ρρ Rho
Ζζ Zeta	Σσ Sigma
Ηη Eta	Ττ Tau
Θθ Theta	Υυ Upsilon
Ιι Iota	Φφ Phi
Κκ Kappa	Χχ Chi
Λλ Lambda	Ψψ Psi
Μμ Mu	Ωω Omega
Obsolete letters
Ϝϝ Digamma	Ϙϙ Qoppa
Ϛϛ Stigma	Ϡϡ Sampi
Ϻϻ San	Ϸϸ Sho
Greek diacritics

Omicron (uppercase Ο, lowercase ο, literally "small o": o mikron, micron meaning 'small' in contrast to omega) is the 15th letter of the Greek alphabet. In the system of Greek numerals it has a value of 70. It is not used in mathematics because it is indistinguishable from the Latin letter O. Indeed, it is not widely used because of confusion with the digit 0. This letter is equal to the Phoenician letter Ayin. It is also most similar to the modern English letter O, as in 'hot'.

In Unicode the capital letter is codepoint U+039F and the lowercase is U+03BF.

The upper-case letter of omicron (O) was originally used as a symbol for

• The Big O notation, representing the asymptotic rate of growth of a function in mathematics.

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