Deteriorated to the west or east (4)
I believe the answer is:
wore
'deteriorated' is the definition.
(wearing is a kind of deteriorating)
'the west or east' is the wordplay.
'the west' becomes 'W' (abbreviation).
'east' becomes 'e' (abbreviation).
'w'+'or'+'e'='WORE'
'to' acts as a link.
(Other definitions for wore that I've seen before include "Had on (clothes)" , "Was clothed in" , "Sported, put on" , "Eroded" , "Was clad in" .)