Understood attic collapsed (5)
I believe the answer is:
tacit
'understood' is the definition.
(thesaurus)
'attic collapsed' is the wordplay.
'collapsed' is an anagram indicator.
'attic' with letters rearranged gives 'TACIT'.
(Other definitions for tacit that I've seen before include "Implied, unstated" , "Implied, not spoken" , "Aircraft engine casing" , "Unvoiced" , "Understood, implicit" .)