Faith
Etymology
From Latin “fides” (trust, confidence, good faith), via Old French “feid.” The same root gives “fidelity,” “confide,” and “fiduciary,” all turning on trust rather than evidence. This is why faith so naturally names loyalty between people (“keeping faith”) as well as religious commitment.
noun · /FAYTH/
Trust or commitment held firmly, especially where it goes beyond available proof.
What it names
Allegiance and trust as an act of will, not just an estimate of what is likely true.
Example
Starting the company took a kind of faith the spreadsheet couldn’t justify — a bet on people, not numbers.
Related idea
Belief is holding a proposition to be true; faith is closer to trust and commitment — an act of the will that can persist even where belief wavers.