| Term | Description |
| Unde, Undy | Waving or wavy. This term is applied to ordinaries or lines of division. |
| Unescutcheoned | Without an escutcheon; without a coat of arms |
| Unglued | Having hoofs of a tincture different from that of the body. (Said of a horse, stag, etc.) |
| Unifoil | A plant with only one leaf |
| Urdee | Pointed. The cross urdee is an ordinary cross with the ends drawn to a sharp point instead of being cut straight. |
| Urinant | The opposite of haurient. The term is applied to the dolphin or other fish when represented with the head downward and the tail erect |
| Urvant | Turned or bowed upward |