The best way to resolve a definition dispute is by consulting dictionaries, rather than framing the dispute as an EL&U question. Dictionaries are great resources for "verifying the definitions" of words, whereas asking this sort of thing as an EL&U question seems more like soliciting individual opinions. Such "what's-your-take" questions may run afoul of these sentiments, found in the FAQ:
Chatty, open-ended questions diminish the usefulness of our site... Avoid asking subjective questions where...
- every answer is equally valid
- your answer is provided along with the
- there is no actual problem to be solved
- we are being asked an open-ended,
Furthermore, by arguing with your friend about which definition is the "more accurate" one, you miss the greater point. Most words – faith among them – don't have a single definition, and even when you find a word with only one definition, this definition will often vary some from dictionary to dictionary.
In this case, if you look up faith on Wordnik, you'll see that both of you are right! The only thing wrong about your stance is insisting that your friend is wrong in his definition of the word; he's no less right than you are. The two of you are merely emphasizing different nuances of the word, where it can be used in varying contexts.
(this additional information answers a follow-on question posed to me by the O.P. in a comment below):
I don't see "an unwavering sticking to of a belief in the light of concrete proof contrary to and disproving the belief", so if you could point me at which dictionary and entry said that, I'll concede that he is using a version of the word faith that I've never heard before. Otherwise, I can't imagine the word he wanted is faith so much as some other word.
Very well; since I can't answer that in a comment, let me try to answer that here:
Definition 1 (from the conversation):
Any belief not based on evidence and won't change because of evidence.
I thought this mapped (roughly) to (from Wordnik):
Belief that does not rest on logical proof or material evidence.
Definition 2 (from the conversation):
Complete trust or confidence in someone or something
I thought this mapped to (from Wordnik):
Confident belief in the truth, value, or trustworthiness of a person, idea, or thing.
Granted, "won't change because of evidence" (from the conversation) sounds a bit more cynical than "does not rest on logical proof" (from the dictionary), but my main point was that there is a difference between
belief not resting on material evidence or logical proof
complete confidence or trust in something or someone
so there was room for you both to be right.
As for the latest wording (in your comment):
an unwavering sticking to of a belief in the light of concrete proof contrary to and disproving the belief
that sounds more cynical still, but that wasn't part of your question when I composed my original answer. That latest "definition" seems to have a sardonic bias aimed at belittling those adhering to some sort of (presumably religious?) faith, and therefore seems like an informal, personal, sarcastic definition, as opposed to an authoritative and recognized one. I'd put that in the same category as this "definition" of stupidity, often mistakenly attributed to Einstein:
"The definition of stupidity is doing the same thing over and over again and expecting different results."
which is more of a quip than a true definition.