| Subject | English | German |
| zool. | common hydra | Süßwasserpolyp |
| med. | hydra-like animals | Hydrozoen |
| drv. | Hydra-Matic | Hydramatic (automatic transmission developed by GM in the early forties) |
| drv. | Hydra-Matic | Hydra-Matic (automatic transmission developed by GM in the early forties) |