Faith by Definition

This thread got me thinking.We have a word "faithful" which is surely related to "faith".Suppose my friend and I had started on a project. Unfortunately my friend died. By continuing with that project, I would be faithful to my friend. It does not require that I believe he is alive or in heaven. My faithfulness would be in my continued work on that project we started together.Could it be that we have the meaning of "faith" wrong? Maybe to have faith in Sherlock Holmes, is to follow his principles of evidence, and it doesn't matter that he was a fictional character. Maybe we could have faith in the invisible pink unicorn, if only the IPU had left us some principle to follow.Could it be that there is more faith among scientists in their principled investigation of the nature of the world, than there is among those who blindly believe in the literal truth of some ancient stories?

I'm wondering whether the usage of the word has changed over time, and hoping that someone more familiar with the languages and culture of the time can tell us what it meant to the early Christians.