The knife is sharp.

Having a fine edge or point that can cut or pierce easily.
Be careful with that sharp tool.
She used a sharp blade to cut the paper.
The sharp scissors made the job easier.
sharp knife
sharp edge
sharp tool
keen
pointed
cutting
Be careful with that sharp knife.

Having a thin edge or point that can cut or pierce.
The sharp pencil made it easy to write.
She used a sharp pair of scissors to cut the paper.
He felt the sharp pain in his finger.
sharp knife
sharp edge
sharp object
keen
pointed
cutting
The picture on the screen is very sharp.

Clear and strong in sound or image.
The knife is very sharp.
Her memory of the event is sharp.
The music was sharp and lively.
sharp image
sharp sound
sharp focus
clear
distinct
vivid