Instrumentality (6)
I believe the answer is:
agency
'instrumentality' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for agency that I've seen before include "Means - business" , "Business that conducts business on behalf of others" , "Office or business of one who does business for others" , "Organisation providing a particular service" , "Cagney (anag.)" .)