The word “lunar” means something related to the Moon. It can describe anything connected with the Moon, influenced by it, resembling it or measured by its cycles.
The word entered English through Middle English and Old French from the Latin lunaris, meaning “of the moon.” Latin luna meant “moon,” and the same root appears in terms such as lunation, the Moon’s cycle of phases, and selenology, the scientific study of the Moon.
In astronomy, common phrases include lunar surface, lunar eclipse and lunar orbit. A lunar month is based on the Moon’s cycle, although different scientific and calendar definitions use slightly different periods. The synodic month, from one new moon to the next, lasts about 29.5 days.
Lunar does not mean “night-time” or “about the Sun.” The related word solar refers to the Sun. Also, “lunar” can describe an Earth-based calendar system that follows the Moon, while “moon” itself is the everyday noun for Earth’s natural satellite and, more broadly, for natural satellites orbiting other planets.