a discourse for the purpose of religious instruction or exhortation, especially one based on a text of Scripture and delivered by a member of the clergy as part of a religious service.
2.
any serious speech, discourse, or exhortation, especially on a moral issue.
Origin: 1150–1200; Middle English < Medieval Latin sermōn- (stem of sermō) speech from pulpit, Latin: discourse, equivalent to ser- (base of serere to link up, organize) + -mōn- noun suffix
c.1200, from Anglo-Fr. sermun, O.Fr. sermon, from L. sermonem (nom. sermo) "discourse, speech, talk," originally "a stringing together of words," related to serere "to join" (see series). Main sense in Eng. and Fr. is eliptical for L. sermo religiosus. Dim. form sermonette is attested from 1814.