Faith

Latin fides — trust, confidence, reliance. Related to fidere — to trust. Root of fidelity, fiduciary, confide. Originally about trust in a person or promise before it became attached specifically to religious belief.

The narrowing of 'faith' to mean specifically religious belief happened gradually. 'Faith community,' 'faith-based' — these are modern coinages. The original Latin sense survives in legal and financial language: fiduciary duty, bona fide, confident.