Knock up as usual (3)
I believe the answer is:
rap
'knock' is the definition.
(synonyms)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for rap that I've seen before include "Sort of music" , "Knock sharply" , "Short quick tap" , "Knock - punishment - monologue to music" , "Smack (knuckles)" .)