Cross threshold turning up (4)
I believe the answer is:
rood
'cross' is the definition.
(rood is a kind of cross)
'threshold turning up' is the wordplay.
'threshold' becomes 'door' (I've seen this before).
'turning up' shows that the letters should be reversed in order.
'door' reversed gives 'ROOD'.
(Other definitions for rood that I've seen before include "Crucifix on door" , "old piece of land" , "Crucifix in entrance, set back" , "Cross, crucifix" , "The Holy . . . . was the Cross of Christ" .)