EXCOMMUNICA'TION, noun The act of ejecting from a church; expulsion from the communion of a church, and deprivation of its rights, privileges and advantages; an ecclesiastical penalty or punishment inflicted on offenders. excommunication is an ecclesiastical interdict, of two kinds, the lesser and the greater; the lesser excommunication is a separation or suspension of the offender from partaking of the eucharist; the greater, is an absolute separation and exclusion of the offender from the church and all its rites and advantages.