The crossword solution for the term HIT, AS THE KNUCKLES is RAP. RAP is a genre of music that originated in the United States in the 1970s. It is characterized by its use of rhythmic beats and rhymes and often contains elements of spoken word poetry. RAP is often associated with hip-hop culture and has become one of the most popular genres of music in the world. The phrase 'hit, as the knuckles' is often used to describe the sound of a rapper's voice when they are rapping.