Rap (3,3)
'rap' is the definition.
(I know that knock is a more specific form of rap)
This is the entire clue.
(Other definitions for knock that I've seen before include "Criticise; rap" , "Bump" , "Setback; thirteen across" , "Rap on door?" , "Sharp blow, perhaps on door" .)
'rap' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for hip hop that I've seen before include "Genre of 1980s and '90s African-American music" , "Kind of pop music" , "Rap music" .)