Wake-up call dislodging one initially reluctant partygoer (8)
I believe the answer is:
reveller
'partygoer' is the definition.
(I've seen this before)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for reveller that I've seen before include "One who carouses or parties" , "A carouser, out on the town" , "Merrymaker, loud party-goer" , "Carouser, merrymaker" , "Noisy party-goer" .)