Wedge book upright (4)
I believe the answer is:
jamb
'upright' is the definition.
(I know that jamb is a type of upright)
'wedge book' is the wordplay.
'wedge' becomes 'jam' (I've seen this in another clue).
'book' becomes 'b' (abbreviation for book).
'jam'+'b'='JAMB'
(Other definitions for jamb that I've seen before include "Side post of a doorway" , "Door sidepiece" , "Upright of door" , "Vertical member of door frame" , "Door-frame side" .)