1. reliance on the integrity, strength, ability, surety, etc., of aperson or thing; confidence.
2. confident expectation of something; hope
The fundamental basis of any sort of relationship is usually trust whether it be friendship, courtship, family relationship etc.
Trust is developed throughout the relationship and is gradually built up to form some sort of a reliance or confidence towards another. However have you ever wondered why this sort of trust is so easily broken even if its a little single thing they do that will cause you to realise that trusting them was wrong ?
Think of it this way, trusting a person is sort of like a perpetual risky investment. You commit to it and put your efforts into it, the same as you invest money into some sort of capital. Then you expect them to trust you as well, sort of like the returns of an investment. The dividends are the benefits you gain from trusting them eg having them as a good friend/wife/brother, them being there for you, or maybe just happily chatting with them. All is good until you find out that your investment is rapidly declining in value, that is the person you trust has done something that makes you doubt yourself as to why you trusted them in the first place.