What's the noun for knifeboard? Here's the word you're looking for.
knife
A utensil or a tool designed for cutting, consisting of a flat piece of hard material, usually steel or other metal (the blade), usually sharpened on one edge, attached to a handle. The blade may be pointed for piercing.
A weapon designed with the aforementioned specifications intended for slashing and/or stabbing and too short to be called a sword. A dagger.
Any blade-like part in a tool or a machine designed for cutting, such as that of a chipper.
(historical, attributive) A way of arranging benches back to back, resembling a knifeboard; common on the open upper deck of early double-deck omnibuses and trams.
(historical, by extension) An early bus with narrow, restrictive seating; a knifeboard bus.