"Wait on" vs "wait for"
I've just heard
your sister is waiting on you
with the meaning of wait for (as in wait for the bus).
Up to now I had only encountered wait on with the meaning of attend to / serve.
Is this use of wait on instead of wait for widely spread in the English speaking world or more specific to certain geographical areas?
In the sentence I'm quoting above, and without further context, could there be any ambiguity as to the meaning?
It's regional in U.S. English. Much of the U.S. says "waiting for you", but I believe that much of the South says "waiting on you". I don't know exactly what regions use "wait on" (not the Northeast), and a couple of minutes of Googling didn't find any answers, so I can't be more specific.
Wait on has numerous meanings. In the OP’s example, it means, in the words of the OED’s definition, ‘remain in one place in expectation of’, in other words, wait for. The OED’s citations supporting this sense range from 1694 to 1984. The OED gives no indication of regional bias, but I wouldn’t say the use was ‘widely spread’. As for ambiguity, most of the time context removes it, and I would say it would generally do so in this case.
"Wait on" as a synonym for "wait for" is something I've heard much more in US English than British English, but it is used in that sense. They're pretty much synonymous. And yes, you're right that the sentence "your sister is waiting on you" is ambiguous, and so it's probably best to avoid using the colloquial "wait on" for this meaning.