sigma

[n] - the 18th letter of the Greek alphabet
Found on http://www.webdictionary.co.uk/definition.php?query=sigma

sigma

noun the 18th letter of the Greek alphabet
Found on http://wordnetweb.princeton.edu/perl/webwn?s=sigma

Sigma

Sigma is a cultivated variety of potato.
Found on http://www.probertencyclopaedia.com/browse/QS.HTM

Sigma

Parameter expressing the seawater density
Found on http://www.superglossary.com/Glossary/Science/Marine_Biology/
No exact match found