Tiny reel destroyed completely (8)
I believe the answer is:
entirely
'completely' is the definition.
(synonyms)
'tiny reel destroyed' is the wordplay.
'destroyed' is an anagram indicator.
'tiny'+'reel'='tinyreel'
'tinyreel' is an anagram of 'ENTIRELY'.
(Other definitions for entirely that I've seen before include "Fully or absolutely" , "Without reservation" , "'Fully, wholly (8)'" , "Wholly and completely" , "Wholly, totally" .)