"Laity" derives from the Greek "laikos"

[Neos]

Etymology of "laity"

The word laity (the body of religious worshipers, as distinguished from the clergy), comes from the French laite from the late Latin laicus, which is a transliteration of the Greek laikos (of the people; λαϊκός) from laos (people; λαός).

From the same root:
Lay, layman

In Greek
a) laos: people [λαός]
b) laikos: of the people, folk, vulgar [λαϊκός]

More: http://ewonago.blogspot.com/ [English Words of no Apparent Greek Origin]