Why was "tantrum" trending last week?
18th letter of the Greek alphabet, corresponding to Latin S, a metathesis of Hebrew samekh. In uncial writing, shaped like an S or a C.
The Greek letter sigma. Entries beginning with this character are alphabetized under sigma.
The symbol for reflection coefficient.
The symbol for standard deviation.
sigma sig·ma (sĭg'mə)
Symbol ς The 18th letter of the Greek alphabet.