Is “Sigma” a Scrabble word?
Yes
SIGMA
Valid in at least one Scrabble dictionary
Valid in these dictionaries
SOWPODS / CSW
Scrabble UK & International
TWL / NWL
Scrabble North America
Large English Dictionary
General English word list
Meaning of Sigma
/ˈsɪɡmə/
noun
1.The eighteenth letter of the Classical and Modern Greek alphabets, the twentieth letter of Old and Ancient.
2.The symbol Σ, used to indicate summation of a set or series.
3.The symbol σ, used to indicate one standard deviation from the mean, particularly in a normal distribution.