six hundred threescore and six
Strong’s Dictionary of Greek Words:
Phonic:
khee xee stig’-ma
Meaning:
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
KJV Usage:
six hundred threescore and six