At last somehow nail the fly, having trapped it (7)
I believe the answer is:
finally
'at last' is the definition.
(synonyms)
'somehow nail the fly having trapped it' is the wordplay.
I cannot quite understand how this works, but
an anagram of 'nail' is 'inal' which is located in the answer.
'the fly' could be 'fly' and 'fly' is present in the leftover letters.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for finally that I've seen before include "At last" , "when all is said and done" , "for ever" .)