The Collaborative International Dictionary
Excubitorium
Excubitorium \Ex*cu`bi*to"ri*um\, n. [LL. excubitorium; ex out + cubare, cubitum, to lie.] (Eccl. Antiq.) A gallery in a church, where persons watched all night.
Wiktionary
excubitorium
n. (context historical English) A gallery in a church, used for all-night vigils.