FROM STRONG’S GREEK DICTIONARY (1890)

Strong’s Greek Dictionary (1890) — public domain, printed whole.

chi χξϛ — xi stigma {khee xee stig'-ma — the 22nd, 14th and an obsolete letter (4742 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 for 4742