Latin term for the open space left in the roof of the atrium of a Roman house (domus) for lighting it and the rooms round.[10]
• (n.) A space left unroofed over the court of a Roman dwelling, through which the rain fell into the impluvium or cistern.
(from the article `atrium`) ...a marble basin known as the impluvium, which was situated in the centre of the room under the opening in the roof called the compluvium.
Com·plu'vi·um noun [ Latin ] (Architecture) A space left unroofed over the court of a Roman dwelling, through which the rain fell into the impluvium or cistern. 
A compluvium was a space left unroofed over the court of a Roman dwelling, through which the rain fell into the impluvium or cistern.
compluvium An open space over the atrium of a Roman house through which the rain flew into the impluvium or cistern (Roman antiquity).