Pestle is both a noun (the object) and a verb (an action) "to pestle" is to grind or pound as if with the object.
examples:
Her thoughts were pestled by the constant interruption of Darryl and his obnoxious yappy dog.
You should pestle that before brewing, she said with a smile.
Hand me that pestle, would you?
The vessel with the pestle has the brew that is true.
This mortar needs a finer pestle.
My other pestle is on the trestle.