A jamb is a post that forms the side of a door or window. Jam, which is both a noun and a verb, has many meanings, including (1) to drive or wedge into a tight position, (2) to lock into an unworkable position, (3) to cram, (4) the act of jamming or the condition of being jammed, and (5) a preserve made from boiled and sugared fruit. There are a few other definitions. The relevant point here is that jam never means a post that forms the side of a door or window.
Examples
Jam is often misused in place of the less common jamb—for example:
Don’t use the number on the side of the tire—check the driver’s side door jam or owner’s manual. [Wausau Daily Herald]
Sgt. Gregg Owens and Ptl. Robert Thompson discovered the door had been forced open, damaging the door jam. [NJ.com]
These writers get it right:
Damages to the door and door jamb were estimated at $1,000. [Peabody Gazette-Bulletin]
There it was, a back door that had been kicked in, the lock unmoored from the door jamb, the jamb’s wood in splinters. [Chicago Tribune]
And for good measure, here are a few examples of jam used correctly:
But Force says he was in Victoria on Thursday morning, nowhere near the traffic jam south of Vancouver. [CBC]
There was homemade “rhuberry” (rhubarb and strawberry) jam at breakfast. [Guardian]
But as she reached into the machine to remove a jammed clip, she accidentally pressed down on the machine’s foot pedal … [New Zealand Herald]
