み

み turns an adjective into a noun for a quality you feel or sense: a taste, a pain, an emotion, a tinge. Drop the い of an い-adjective and add み; a few な-adjectives take it directly.

み or さ

さ works on almost any adjective and gives the degree: how sweet, how warm, how big. み works on a limited set and gives the quality as something you sense in a thing, or a touch of it.

For a size, a speed or anything else you measure, only さ works.

• × 大きみ → 大きさ
• × 速み → 速さ

Words to learn as words

Many み-nouns have meanings of their own. たのし楽しみ is "something to look forward to", and たのし楽しみです is how you say you are looking forward to it. つよ強み and よわ弱み are a strong point and a weak point.

With colours and shapes, み is "a tinge of": あか赤み is reddishness, まる丸み roundness.