Definitions
1.NounThe eighteenth letter of the Classical and Modern Greek alphabets (Σ, σ), the twentieth letter of Old and Ancient.
2.NounThe symbol Σ, used to indicate summation of a set or series.
3.NounThe symbol σ, used to indicate one standard deviation from the mean, particularly in a normal distribution.
4.NounA sigma male (a self-reliant and assertive male).
5.AdjectivePossessing characteristics of a sigma male.