Final one to finish admitted not being this, as the saying goes? (5)
I believe the answer is:
least
'not being this as the saying goes?' is the definition.
Both the answer and definition are adverbs. Maybe you can see a link between them that I don't see?
'final one to finish admitted' is the wordplay.
'final' becomes 'last' (synonyms).
'to finish' suggests the final letters.
'admitted' means one lot of letters goes inside another (inserted letters get admitted).
The last letter of 'one' is 'e'.
'last' going around 'e' is 'LEAST'.
Can you help me to learn more?
(Other definitions for least that I've seen before include "Lowest or smallest" , "Steal (anag)" , "Most insignificant" , "Smallest in amount or degree" , "Minimum" .)