"Rap"
To the best of my knowledge, I know of three ways this word can be used:

1. A sharp tap with something (a rap on the knuckles)
2. To talk, also the basis of the eponymous musical genre (his rap number was great)
3. A charge (he was arrested on a felony rap)

Are there any others?

Question

"Rap"
To the best of my knowledge, I know of three ways this word can be used:

1. A sharp tap with something (a rap on the knuckles)
2. To talk, also the basis of the eponymous musical genre (his rap number was great)
3. A charge (he was arrested on a felony rap)

Are there any others?

Answer

4 rap to blurt out a compliant sharply: related to your number 2
5 rap to criticise or to blame related to your number 3
6 rap to complain in a rapping manner, "i tol y n to com an" --> and so an repeatedly insistently, incessantly, continually.
7 rap a rapping sound 
8 rap to rap on the door [knock quickly and loudly in a repetitive manner, like how an angry person would knock on a door , or the police] 
9 rap to arrest, detain, convict.

all stemming from you three meanings and some are a little archaic

Answer

Ah yes, I've seen that too. Thanks Greg! Seems synonymous with "a lousy deal"

Answer

I've heard a few slang expressions using it. "He got a bum rap at work" is one example. Context: He did a minor infringement at work and they fired him for it. I could say ... "He got a bum rap at work" meaning "He was treated unfairly".