- unofficial
- unorganized
- unorganized ferment
- unorganized virus
- unorientation
- unrest
- unripe cataract
- unsaturated
- Unschuld's sign
- unsex
- unsound
- unstable confectio
- Unstriated
- unstriated muscle, unstriped muscle
- ununited
- Ununited Fracture
- Unverricht's disease
- unwell
- unwholesome
- Upas