High-rise building (5,5)
I believe the answer is:
tower block
'high-rise building' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for tower block that I've seen before include "Tall residential or office building" , "high-rise building" , "Tall building of offices, flats" , "Skyscraper" , "big build-up?" .)