bastille

[French, from Old French, fortress, alteration of bastide, from Old Provençal bastida, from bastir, to build, of Germanic origin.]

1. A fortification or castle, frequently used as a prison.
2. A tower or bulwark in the fortifications of a town.

1. As bastion (1).

2. Fortified tower.

3. Small fortress.

4. Name of the C14 Parisian prison-fortress destroyed in 1789, so synonymous with a gaol.

The noun has one meaning:

Meaning #1: a jail (literally, a French jail)