noun

blade

BLAYD/bleɪd/

A broad, thin projecting part with a defined edge.

The knife's broad steel blade ends in a sharply defined cutting edge.

A close view of a kitchen knife emphasizing its broad, flat steel cutting blade, with the handle visually subordinate and the sharpened edge clearly visible.

Etymology

The original image is a leaf: the word already described leaf-like parts of implements. That flat, broad shape connects the plant meaning to the cutting part of a knife or sword.

In context

mahalodotcom1:19

my knife and I'm going to start to cut off this rounded piece right here and make a nice flat piece I'm going to look down the back of the blade

Knife Skills - How to Julienne a Potato

More examples

She sharpens the knife’s blade before slicing the bread.
A single blade of grass bends under the drop.
Her backpack rubs against one shoulder blade.

Forms

blade · blades

propeller noun — Rotating device that pushes against air or water.

rotor noun — Rotating assembly of blades on a helicopter.

Similar words

vane: Usually guides or redirects airflow rather than actively pushing it.
paddle: Often names the whole tool, including its handle and blade.