Objection over resonant sound from part of posterior? (7)
I believe the answer is:
buttock
'part of posterior?' is the definition.
'buttock' can be an answer for 'part' (buttock is a kind of part). I am unsure of the 'of posterior?' bit.
'objection over resonant sound' is the wordplay.
'objection' becomes 'but' (as in 'no ifs, no buts').
'over' means one lot of letters go next to another (in a down clue, some letters go over others).
'resonant sound' becomes 'tock' (I can't justify this - if you can you should believe this answer much more).
'but'+'tock'='BUTTOCK'
'from' acts as a link.
Can you help me to learn more?
(Another definition for buttock that I've seen is " Single cheek".)