how do you use the word "fan wai"

[Rik]

How does one use the word "fan wai" like in a sentence. I hear people saying "fan wai," as if it's like a preposition or conjunction or something. Give me some examples of different usages of "fan wai" if anyone can. Thank you.

[???]

反胃?
發圍?
範圍?

[???]

反胃?
發圍?
範圍?
but none of the above is a preposition or conjunction bor!!!

[%sig%]

[kelly]

Then what do these "faan wai" mean?

[Terence]

faan2 wai4 反為. on the contrary, whereas