Plain English Meaning

Tiny drops of water in the clouds that are colder than freezing but somehow still liquid. The moment they hit something — like a wing — they instantly turn to ice.

Full Definition

Liquid water droplets that remain in liquid form at temperatures below freezing (0°C / 32°F). They are unstable, and freeze on contact when they strike an aircraft surface, forming structural ice.

Context Anchor

Seen in instrument flying and weather discussions about structural icing in clouds, freezing drizzle, and freezing rain.

Derivation

‘Super-cooled’ means cooled below the without actually freezing. The prefix ‘super-’ here comes from Latin meaning ‘beyond’ — so ‘beyond cooled,’ i.e., cooled past you'd expect freezing to occur. This helps why the droplets are unstable: they are past the point where they should be ice, and the smallest (like striking a wing) triggers freezing.