Spoiling a lot with new nail (5)
I believe the answer is:
talon
'nail' is the definition.
(thesaurus)
'spoiling a lot with new' is the wordplay.
'spoiling' indicates anagramming the letters.
'with' means one lot of letters go next to another.
'new' becomes 'n' (abbreviation as in New Testament NT).
'a'+'lot'='alot'
'alot' with letters rearranged gives 'talo'.
'talo'+'n'='TALON'
(Other definitions for talon that I've seen before include "Tonal (anag.)" , "Bird's claw" , "Hooker" , "Bird of prey's claw" , "Hooked claw; cards left after deal" .)