A common 8-letter word that means cosh is "bludgeon."
A four letter word meaning not kosher is: tref
I will bludgeon you with this bat.
The word pine can have that meaning.
A four-letter word for cooking fat is "lard".
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.
I pulled out my gun when I saw the man's rather large bludgeon. I was concerned that he might bludgeon me to death.
Rend is a four letter word that means to tear into pieces. Tear is also a four letter word meaning to pull apart.
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".