This title probably comes from the Hebrew expression for the high priest, hakkohen haggadol (Num. 35:25-32), which literally means “great priest.” The King James Version does not note the distinction, rather it uses the most common English title, High Priest.
Great Priest in Greek:
Strong’s Concordance numbers: 2409, 3173
Bible reference: Heb. 10:21 (not KJV)
Since we have a great priest over the house of God, let us draw near to God with a sincere heart and with the full assurance that faith brings, having our hearts sprinkled to cleanse us from a guilty conscience and having our bodies washed with pure water. (Hebrews 10:21-22 NIV)