Borrowed from Latin compluvium.

compluvium (plural compluvia)

1. (architecture) A space left unroofed over the court of a dwelling in Ancient Rome, through which the rain fell into the impluvium or cistern.
   • 1881, William Audsley, Popular Dictionary of Architecture and the Allied Arts: Aquila to Baptisterium:

     In the centre of the floor of the atrium a portion was sunk for the reception of rain water; this was termed the impluvium; and above it an opening of similar dimensions was left in the ceiling or roof, termed the compluvium.

From compluit (“it flows together, it rains upon”) +‎ -ium, from cum + pluit (“it rains”).

• (Classical Latin) IPA^(key): /komˈplu.u̯i.um/, [kɔmˈpɫ̪uː̯iʊ̃ˑ]
• (modern Italianate Ecclesiastical) IPA^(key): /komˈplu.vi.um/, [komˈpluːvium]

compluvium n (genitive compluviī or compluvī); second declension

1. A rectangular open space in the middle of a Roman house, which collected rain water falling on the surrounding roof and conducted it to a basin (impluvium) placed below.

Second-declension noun (neuter).

¹Found in older Latin (until the Augustan Age).

• compluviātus

• impluit
• impluvium
• pluit

• Catalan: compluvi
• → English: compluvium
• Italian: compluvio
• Portuguese: complúvio
• Spanish: compluvio

• “compluvium”, in Charlton T. Lewis and Charles Short (1879) A Latin Dictionary, Oxford: Clarendon Press
• compluvium in Charles du Fresne du Cange’s Glossarium Mediæ et Infimæ Latinitatis (augmented edition with additions by D. P. Carpenterius, Adelungius and others, edited by Léopold Favre, 1883–1887)
• compluvium in Gaffiot, Félix (1934) Dictionnaire illustré latin-français, Hachette.
• “compluvium”, in Harry Thurston Peck, editor (1898), Harper's Dictionary of Classical Antiquities, New York: Harper & Brothers
• “compluvium”, in William Smith et al., editor (1890), A Dictionary of Greek and Roman Antiquities, London: William Wayte. G. E. Marindin