Strong’s Greek
G1858 — heortazo
The entry below is Strong’s own definition (1890, public domain), and every verse where the word occurs.
ἑορτάζω
heortazo — pronounced heh-or-tad'-zo
from 1859; to observe a festival:--keep the feast. see GREEK for 1859
1 occurrence in the KJV.
1 Corinthians 5:8
Therefore let us keep the feast, not with old leaven, neither with the leaven of malice and wickedness; but with the unleavened bread of sincerity and truth.