There are many synonyms for the word "day". Some common ones include "daylight", "sunlight", "morning", "afternoon", and "evening". Other synonyms for "day" are "24-hour period", "diurnal cycle", and "daytime". "Dawn", "dusk", "sun-up", and "sun-down" are also used as synonyms for "day". Additionally, words like "epoch", "era", and "age" can be used as synonyms for "day" when referring to long periods of time. Whatever synonym is used, it ultimately refers to the time between sunrise and sunset, when the sun is visible in the sky.