The story
From mizzle (noun) + -y (suffix forming adjectives from nouns, with the sense ‘behaving like, or having natures typical of [the nouns]’).
Etymology from Wiktionary, CC BY-SA 4.0.
Today it means: Raining in the form of mizzle (“misty rain; drizzle”); drizzly. Full definition →
From mizzle (noun) + -y (suffix forming adjectives from nouns, with the sense ‘behaving like, or having natures typical of [the nouns]’).
Etymology from Wiktionary, CC BY-SA 4.0.