A tux he's ordered to wear out (7)
I believe the answer is:
exhaust
'wear out' is the definition.
(exhausting is a kind of wearing out)
'a tux he's ordered' is the wordplay.
'ordered' indicates anagramming the letters.
'a'+'tux'+'hes'='atuxhes'
'atuxhes' is an anagram of 'EXHAUST'.
'to' acts as a link.
(Other definitions for exhaust that I've seen before include "Gases ejected from an engine" , "Devitalize, drain of energy" , "Waste gas from engine" , "Tire out - waste gases from engine" , "lower part of estate?" .)