Favouring penny-pinching world leader is a no-no (9)
I believe the answer is:
forbidden
'is a no-no' is the definition.
(a no-no is something forbidden or not allowed)
'favouring penny-pinching world leader' is the wordplay.
'favouring' becomes 'for' (I've seen this before).
'penny' becomes 'd' (abbreviation e.g. Lsd - pounds, shillings, pence).
'pinching' is an insertion indicator (some letters are taken or pinched).
'world leader' becomes 'Biden' (Joe Biden).
'd' placed into 'biden' is 'bidden'.
'for'+'bidden'='FORBIDDEN'
(Other definitions for forbidden that I've seen before include "Illicit pleasure" , "Prohibited, taboo" , "Proscribed" , "Not allowed, banned" , "Disallowed, banned" .)