Building threat wasted energy (7)
I believe the answer is:
theatre
'building' is the definition.
(theatre is a kind of building)
'threat wasted energy' is the wordplay.
'wasted' indicates an anagram.
'energy' becomes 'e' (physics symbol as in E=mc2).
'threat' anagrammed gives 'theatr'.
'theatr'+'e'='THEATRE'
(Other definitions for theatre that I've seen before include "Scene of plays" , "Globe, say" , "The rate (anag.)" , "war zone" , "World of drama" .)