Halcyon

Halcyon is a pretty word. It sounds Greek. In common use it has several distinct but similar senses according to dictionary.com:

1. calm; peaceful; tranquil: halcyon weather.
2. rich; wealthy; prosperous: halcyon times of peace.
3. happy; joyful; carefree: halcyon days of youth.

The word derives from the Greek alkyon, meaning kingfisher. What? Kingfishers seems irrelevant. But Greek mythology strikes again; the American Heritage Dictionary explains that the halcyon was

A fabled bird, identified with the kingfisher, that was supposed to have had the power to calm the wind and the waves while it nested on the sea during the winter solstice.

In Greek mythology Alcyone (or Halcyon) was the daughter of Aeolus, ruler of the winds. She and her husband got turned into kingfishers after some bad run-ins with various gods. Halcyon is used today to refer to a family of kingfishers.