Actually, rather can mean a reduction in the strength of a meaning, but it can also mean an increase!
Either way, this word causes the strength to shift only a shade each way. Because of this, rather is usually more than a little or a bit, but less than quite.
For example, to say that someone is rather shy, means that they are shy to a noticeable amount. If the person is being polite (an action that has the most confusing effect on the English language), then rather shy might mean very shy.
"I was rather annoyed when the van pulled out right in front of me."
In the sentence above, the speaker is shading their annoyance: it is considerable yet controlled.
"Would yo like another whiskey?"
This is rather old-fashioned (i.e. notedly). The interjection rather means "yes, certainly, of course".
I hope that makes sense...
"Poetry is that which gets lost in translation" — Robert Frost