Being dependant has to do with relying on something. Many people are dependant on coffee in the morning, while a dependant is someone who relies on you for financial support.
Don't be confused by the spelling: in the UK they use the ant ending, and in the US, ent is more popular. Either way, this word has to do with reliance. Kids are dependants of their parents, since they rely on them for food and shelter. A drug addict is dependant on drugs. And if a decision is dependant on your mood, that means it depends on or will be decided by how you feel.
