“Your confidence that another will act with a necessary degree of reciprocity (mutually beneficial) for the matter at hand, despite the opportunity to act out of an equal degree of self interest.”
This definition addresses the spectrum of low trust exchanges to consanguineous interactions to high trust mutual insurance. Most definitions assume an equality of relations that never actually exists and as such those other definitions always seem wanting.
It also explains when we are actually trusting someone, versus asking for a donation. Trust is a matter of reciprocity given the relationship you have to someone else.