Which word describes someone who is confidently optimistic and cheerful?

The word "sanguine" is derived from the Latin word "sanguis," meaning blood, historically associated with a ruddy complexion that suggests health and vitality. In modern usage, "sanguine" describes an individual who exhibits a confident optimism and cheerfulness, particularly in challenging situations. This character trait often involves a hopeful and positive outlook on life, embracing potential good outcomes even in adversity.

The other options don't convey the same meaning. For example, "satiate" refers to being fully satisfied or filled, typically in the context of appetite. "Saturnine," on the other hand, means gloomy or morose, which is quite the opposite of cheerful. "Seine" is related to a type of fishing net and does not pertain to personality traits at all. Thus, "sanguine" stands out as the appropriate term to describe someone who embodies a bright and optimistic disposition.