5516. chi xi stigma (khee xee stig'-ma)

the 22nd, 14th and an obsolete letter (stigma as a cross) of the Greek alphabet (intermediate between the 5th and 6th), used as numbers; denoting respectively 600, 60, and 6; 666 as a numeral

six hundred threescore and six.

see GREEK stigma

StrongsNumbers.com