Slab of glass is tiresome thing we hear (4)
I believe the answer is:
pane
'slab' is the definition.
(thesaurus)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for pane that I've seen before include "Panel of glass" , "Single sheet of glass in a window" , "Piece of glass in window" .)