A dandy and a bore to boot (2,4)
I believe the answer is:
as well
'to boot' is the definition.
(I've seen this before)
'a dandy and a bore' is the wordplay.
I cannot really understand how this works, but
'a' is found in the answer.
'dandy' could be 'swell' (both can informally mean excellent or satisfactory) and 'swell' is found in the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for as well that I've seen before include "Also, in addition" , "on top" , "A swell sort of addition" , "To boot" , "Appropriate" .)