Definition of knock
(noun)
the
sound of knocking (as on a
door or in an
engine or bearing); "the knocking grew louder"
rap with the knuckles; "knock on the door"
knock against with
force or violence; "My car bumped into the tree"
sound like a car
engine that is
firing too early; "the car pinged when I put in low-octane gasoline"; "The car pinked when the
ignition was too far retarded"