Measure up the door (4)
I believe the answer is:
rood
'measure' is the definition.
(thesaurus)
'up the door' is the wordplay.
'up' is a reversal indicator (in down clue: letters go upwards).
'door' in reverse letter order is 'ROOD'.
(Other definitions for rood that I've seen before include "Crucifix on part of an acre" , "Crucifix in church; one quarter of an acre" , "Cross, crucifix" , "Old land measure and large cross in a church" , "Crucifix; old land area measure" .)