Dreadful delay involving Queen worried sufficiently (10)
I believe the answer is:
'sufficiently' is the definition.
'dreadful delay involving queen worried' is the wordplay.
'dreadful' is an anagram indicator.
'involving' is an insertion indicator.
'queen' becomes 'qu' (abbreviation for queen).
'worried' becomes 'ate' (something worrying may eat someone up).
'delay' is an anagram of 'adely'.
'adely' placed around 'quate' is 'ADEQUATELY'.
(Other definitions for adequately that I've seen before include "Sufficiently", "Passably", "Enough", "to satisfy", "In satisfactory manner".)