Kelvin and Duke, say, pirouetting to bop (4)
I believe the answer is:
bonk
'bop' is the definition.
(synonyms)
'kelvin and duke say pirouetting' is the wordplay.
'kelvin' becomes 'k' (abbreviation for the unit of temperature).
'and' means one lot of letters go next to another (I've seen this in other clues).
'duke say' becomes 'nob' (term for a high-status person - eg a duke).
'pirouetting' shows that the letters should be reversed in order (pirouette is a spin in ballet - letters spin round).
'nob' written backwards gives 'bon'.
'k' after 'bon' is 'BONK'.
'to' is the link.
(Another definition for bonk that I've seen is " Hit hard (on the head?)".)