Livery stable (7)

I believe the answer is:

uniform

This clue is a double definition.

'livery' is the first definition.
(thesaurus)

'stable' is the second definition.
(thesaurus)

(Other definitions for uniform that I've seen before include "Unchanging, showing no variation" , "Regimentals" , "Official attire" , "Always the same, unvarying." , "dress of a serving girl?" .)

I've seen this clue in The Guardian, The Times, the Irish Times (Crosaire) and The Telegraph.

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