Beam over a door (6)
I believe the answer is:
lintel
'beam over a door' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for lintel that I've seen before include "Support over a door or window" , "Horizontal beam over a doorway" , "Horizontal piece of timber or stone over a door" , "It's found above the door" , "Supporting member" .)