I don't think it's possible to get theists to agree to a single definition of the word "faith," which is why I prefer to use the word "belief" even though it's not the same. I can remember when I was a believer and I could define faith any number of ways depending on which definition was most convenient. And I was quite sincere about it, as I think many believers are. I think it's an attempt to get out from under the definition that states that it's "belief without proof." I never saw it that way as a believer, even though that is what it was.
Frankly, even if you do get them to define it, I'll bet that most of them will re-define it the moment it becomes necessary to do so to protect their belief system.