Moving staircase ruining earl's coat (9)
I believe the answer is:
escalator
'moving staircase' is the definition.
(synonyms)
'ruining earl's coat' is the wordplay.
'ruining' indicates an anagram.
'earls'+'coat'='earlscoat'
'earlscoat' is an anagram of 'ESCALATOR'.
(Other definitions for escalator that I've seen before include "financial clause" , "Mechanised staircase" , "nonstop flight" , "Carol eats (anag.)" , "it moves up and down" .)