It's in a jamb (4)
I believe the answer is:
door
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">it's in a jamb</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for door that I've seen before include "Jim Morrison?" , "Entrance barrier" , "Moveable structure at an entrance" , "Hinged barrier" , "Threshold" .)