You've really misunderstood, I'm afraid. The Knight is more than just a component of a Trebuchet piece, it really is the kernel of that entity, upon which the Trebuchet functions build. The Knight, it is true, is little use without a Trebuchet or some other manner of catapult. The Trebuchet is what completes the Knight into a fully functional piece. And it is indeed a marvel of engineering and not to be taken for granted. But the Trebuchet without a Knight to fling, is a motive without an object. It is a collection of engineering genius with the function of an incorporeal doorstop. In fact many other strategies are added onto the Knight, together with the Trebuchet, to make it truly strategic. But the Knight is the true kernel of the piece.

That is why, though not wanting to diminish the great contribution of the Trebuchet, I think for a short name for the piece as a whole, Knight is appropriate.

Now, if we talk about the EnPassant/Pawn, on the other hand...