Strong’s Greek
G3006 — leios
The entry below is Strong’s own definition (1890, public domain), and every verse where the word occurs.
λεῖος
leios — pronounced li'-os
apparently a primary word; smooth, i.e. "level":--smooth.
1 occurrence in the KJV.
Luke 3:5
Every valley shall be filled, and every mountain and hill shall be brought low; and the crooked shall be made straight, and the rough ways shall be made smooth;