Rarity, possibly, to accept objection regarding appreciative gesture (9)
I believe the answer is:
tributary
'regarding appreciative gesture' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
'rarity possibly to accept objection' is the wordplay.
'possibly' is an anagram indicator.
'to accept' is an insertion indicator.
'objection' becomes 'but' (as in 'no ifs, no buts').
'rarity' is an anagram of 'triary'.
'triary' placed around 'but' is 'TRIBUTARY'.
Can you help me to learn more?
(Other definitions for tributary that I've seen before include "It helps create a larger flow" , "River flowing into a larger one" , "River flowing into another" , "revenue from clients" , "River feeding a larger one" .)