Strong’s Greek
G2204 — zeo
The entry below is Strong’s own definition (1890, public domain), and every verse where the word occurs.
ζέω
zeo — pronounced dzeh'-o
a primary verb; to be hot (boil, of liquids; or glow, of solids), i.e. (figuratively) be fervid (earnest):--be fervent.
2 occurrences in the KJV.
Acts 18:25
This man was instructed in the way of the Lord; and being fervent in the spirit, he spake and taught diligently the things of the Lord, knowing only the baptism of John.
Romans 12:11
Not slothful in business; fervent in spirit; serving the Lord;