Serein
From Glossary of Meteorology
serein
The doubtful phenomenon of fine rain falling from an apparently clear sky, the clouds, if any, being too thin to be visible.
Frequently fine rain is observed with a clear sky overhead, but clouds to windward clearly indicate the source of the drops. Also, it has been defined as fine rain falling from a clear sky after sunset, probably actually referring to dew, a survival of the old belief that dew falls.
