Lewis Short
offertōrĭum | obf- (noun N) : (). , id.
* A place to which offerings were brought, an offertory (eccl. Lat.): offertorium tali ex causā sumpsit vocabulum. Fertum enim dicitur oblatio, quae altari offertur, et sacrificatur a pontificibus, a quo offertorium nomina tur, quasi propter fertum,Isid. Orig. 6, 19.
Charlton T. Lewis, Charles Short, A Latin Dictionary