barrel-vault
vaulted, semi-cylindrical construction used often as roof.

caldarium
Derivative of the Latin verb caleo (= warm up). It is the strongly heated room of Roman baths. Its hot plunge pool was used to take not only a hot bath but also a steam bath due to high levels of humidity. It was also called the "inner room".

cistern
A receptacle for holding rainwater, but also water transported from elsewhere, in order to keep it stored. The cisterns were either covered eiter open, and they could have more than one compartements.

frigidarium
A large cold pool to drop into after enjoying a hot Roman bath (from frigeo). Normally frigidarium has used after a visit to warm rooms (caldarium) or after a training in palaistra. As the largest room in the thermae and often functioned as a hall for social events or communication

tepidarium
The word is derived from the verb tepeo meaning ‘to be tepid’. It is the room of tepid water in the Roman thermae. It was also called middle house or tepid house and was usually situated between the caldarium and the frigidarium. Its main function was the acclimatization of the bather to the change of temperature. Being at the Tepidarium the visitor could also apply ointments on his/her body before or after the hot bath, although, there was a special room for this function called unctorium.