base
The foundation of something can be described as its "base." The base of an object or concept is its fundamental support or underlying structure. It provides stability and strength to the rest of the entity.
The four letter word for repairing something is mend.
A four letter word for something a violinist needs could be Bows.
grip
seat
have
Urge
One such word is evil.
grip
vase
seat
to mend