Synodic period is a term used in astronomy to refer to the time it takes for two celestial bodies to return to the same alignment as seen from the Earth. There are several synonyms that can be used for this term including: - Orbital period: This refers to the time it takes for one celestial body to completely orbit around another. - Lunar month: This is the time it takes for the Moon to return to the same phase as seen from Earth. - Solar month: This is the time it takes for the Sun to return to the same position as seen from Earth. - Sidereal period: This is the time it takes for a celestial body to return to the same position in relation to the stars. - Tropical month: This is the time it takes for the Moon to return to the same position in relation to the Sun.