This as an archaic usage. We don't use 'rub' in this sense in modern English, except when we are quoting the famous line from Shakespeare's Hamlet "There's the rub", meaning the snag or drawback in an idea. This is not something you need to know unless you are reading old texts, and you will never need to use the word in this sense.

'Rub' does have that meaning, although it's old-fashioned and not often used. It's originally from a line in Shakespeare's Hamlet. It can't really be used as a direct replacement for 'problem', its usage is more like variations on an expression. For example, you would never say, "I have a rub," the same way you would say, "I have a problem." Instead, you would say, "...here/there's the rub,", "...that's the rub,", or even the very old-fashioned "...therein lies the rub.". Here's a website with a couple of examples: http://idioms.thefreedictionary.com/Therein+lies+the+rub You can see this meaning here as number 14 in this dictionary: (http://www.dictionary.com/browse/rub?s=t).

Hi, Yes, the word can be used in this way to suggest a problem, an annoyance at injustice or perhaps more specifically, irritation. So for example, someone might be talking about a colleague and say something like, "the way they always take credit for other people's work really rubs me up the wrong way." Another example being use of the word grate. Although technically this could refer to the action of grating food, or metal covering (like a floor grate) it can also be used to suggest irritation in the same way as rub, in that somebody you know may have an annoying laugh which you might say "is beginning to grate on me."

It is rather archaic English.It means difficulty or problem.

The reference to Shakespeare's Hamlet is the most helpful. In that context, it means "friction", which suggests a difficulty or problem. A basic dictionary definition won't help much; this is a cultural reference.