| a. | 1. | Not to be stormed, or taken by assault; incapable of being subdued; able to resist attack; unconquerable; |
| 1. | (Biol.) Capable of being impregnated, as the egg of an animal, or the ovule of a plant. |
| Adj. | 1. | impregnable - able to withstand attack; "an impregnable fortress"; "fortifications that made the frontier inviolable" |
| 2. | impregnable - impossible to take by storm Synonyms: inexpugnable |