Moonlit means lit by the moon. A moonlit garden, a moonlit walk, the moonlit sea. It is almost always used before a noun and almost always in writing rather than speech.
It is a compound adjective of a productive English type — moonlit, candlelit, sunlit, floodlit — where a light source joins the past participle of light. All of them describe the scene rather than the source. Note that moonlight is the noun and can also be a verb meaning to work a second job at night, which has nothing to do with romance and everything to do with tax.
1adjectivemoonlitLit by the light of the moon.
“They walked back along the moonlit beach.”
synonyms: moonlighted, silvered
moonlit is a quality of light.
From moon + lit. Compare stq mouneljoacht (“moonlit”), West Frisian moanneljocht (“moonlit”), Dutch maanverlicht (“moonlit”), Danish månelys (“moonlit”), Swedish månljus (“moonlit”).
Etymology from Wiktionary, CC BY-SA