Tiny reel demolished altogether (8)
I believe the answer is:
entirely
'altogether' is the definition.
(I know that altogether can be written as entirely)
'tiny reel demolished' is the wordplay.
'demolished' indicates an anagram.
'tiny'+'reel'='tinyreel'
'tinyreel' with letters rearranged gives 'ENTIRELY'.
(Other definitions for entirely that I've seen before include "Without reservation" , "Wholly and completely" , "Completely and absolutely" , "Fully or absolutely" , "Wholly, completly" .)