Periods of decline refer to times of decreased activity or productivity. Ebbs (4 letters) is a noun meaning a gradual decrease in activity or strength, while evenings (8 letters) are the time of day when the sun is setting and the sky is darkening. Sunsets (7 letters) are the daily occurrence when the sun disappears below the horizon, and ebbtides (8 letters) are the low tides that occur twice a day.