A four letter word meaning not kosher is: tref
The word pine can have that meaning.
into
stop or halt is a four letter word meaning the opposite of go.
A four letter word meaning the foundation of something is base.
A four-letter word for cooking fat is "lard".
A four letter word meaning to grow light as the sun rises is dawn.
Wash is a four letter word meaning "to clean with water".
spit
circa
join
Faux.
omen
site
Fake
Well
Zero