Pass a door - terrible state (8)
I believe the answer is:
colorado
'state' is the definition.
(Colorado is an example)
'pass a door terrible' is the wordplay.
'pass' becomes 'col' (col is a term for a mountain pass).
'terrible' indicates an anagram.
'a'+'door'='adoor'
'adoor' anagrammed gives 'orado'.
'col'+'orado'='COLORADO'
(Other definitions for colorado that I've seen before include "American river" , "American state, capital Denver" , "Boulder's state" , "Beetle whose larvae destroy potato plants" , "Denver's state" .)