At last about to nail, flailing about, the fly (7)
I believe the answer is:
finally
'at last' is the definition.
(synonyms)
'to nail flailing about the fly' is the wordplay.
I cannot quite see how this works, but
an anagram of 'nail' is 'inal' which is present in the answer.
'the fly' could be 'fly' and 'fly' is found in the remaining letters.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
'about' acts as a link.
Can you help me to learn more?
(Other definitions for finally that I've seen before include "when all is said and done" , "At last" , "for ever" .)