Very light rain (4)
'very light rain' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for drizzle that I've seen before include "Very light rain, stronger than mist but less than a shower" , "Thin rain" , "Fine rain" , "Shed in fine drops" , "Rain gently" .)
(Other definitions for mist that I've seen before include "Thin layer of fog" , "Fret" , "Cloud; thin fog" , "Watery film" , "Think fog or low cloud" .)