Explanation:

- Sanguinity: Refers to the quality or state of being optimistic, hopeful, or confident about the future.

- Acrimony: Means bitterness or ill-feeling, especially in speech or behavior. It's the opposite of sanguinity.

- Despondence: Refers to a state of low spirits caused by loss of hope or courage. It stands in contrast to optimism and sanguinity.

- Optimism: Is the belief or hope that things will turn out well. It is a direct synonym for sanguinity.

- Distrust: Means doubt about the honesty or reliability of a person or thing. It is unrelated to the concepts of hopefulness or confidence.

Optimism is the most appropriate synonym for sanguinity.