E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Conclave (2 syl.).
A set of rooms, all of which are entered by one common key (Latin, con clavis). The word is applied to the little deal cells erected in some large apartment for the cardinals who meet to choose a new Pope, because the long gallery of the Vatican between the cells and the windows of the palace is common ground to all the conclavists. The assembly itself is, by a figure of speech, also called a conclave.