(sometimes initial capital letter) the offering of the unconsecrated elements that is made to God by the celebrant in a Eucharistic service.
2.
Ecclesiastical.
a.
the verses, anthem, or music said, sung, or played while the offerings of the people are received at a religious service.
b.
that part of a service at which offerings are made.
c.
the offerings themselves.
Origin: 1350–1400; ME offertorie < ML offertōrium place to which offerings are brought, offering, oblation, equiv. to L offer(re) (see offer) + -tōrium-tory2; cf. oblation
"the part of a Mass at which offerings are made," c.1386, from M.L. offertorium "place where offerings are brought," from V.L. offertus, corresponding to L. oblatus, pp. of offerre (see offer). Meaning "part of a religious service" is first recorded 1539; sense of "collection of money" is from 1862.
[aw-fer-tawr-ee, -tohr-ee, of-er-] 
) the offering of the unconsecrated elements that is made to God by the celebrant in a Eucharistic service.