There’s nothing possibly to deny about a respected senior (5)
I believe the answer is:
doyen
'a respected senior' is the definition.
'doyen' can be an answer for 'senior' (I've seen this before). I am unsure of the 'a respected' bit.
'there's nothing possibly to deny about' is the wordplay.
'there's nothing' becomes 'o' (I've seen this in other clues).
'possibly' indicates an anagram.
'about' indicates putting letters inside.
'deny' is an anagram of 'dyen'.
'o' put within 'dyen' is 'DOYEN'.
Can you help me to learn more?
(Other definitions for doyen that I've seen before include "Respected field leader" , "Respected expert" , "Respected senior member" , "Prominent group member" , "Top expert in a field" .)