late 14c., communioun, "participation in something; that which is common to all; union in religious worship, doctrine, or discipline," from Old French comunion "community, communion" (12c.), from Latin communionem (nominative communio) "fellowship, mutual participation, a sharing," used in Late Latin ecclesiastical language for "participation in the sacrament," from communis "common, general" (see common (adj.)).
Used by Augustine, in belief that the word was derived from com- "with, together" + unus "oneness, union." In English, from mid-15c. as "the sacrament of the Eucharist," from c. 1500 as "act of partaking in the sacrament of the Eucharist." From 1610s as "intercourse between two or more."
"a cutting off or casting out from communication, deprivation of communion or the privileges of intercourse," specifically the formal exclusion of a person from religious communion and privileges, mid-15c., from Late Latin excommunicationem (nominative excommunicatio), noun of action from past-participle stem of excommunicare "put out of the community," in Church Latin "to expel from communion," from ex "out" (see ex-) + communicare "to share, communicate," related to communis "common" (see common (adj.)).
1925, from omphalo- + Greek -skepsis, from skeptesthai "to reflect, look, view" (from PIE root *spek- "to observe"). Also omphaloscopy (1931). Used earlier in the sense of "navel-gazer" were omphalopsychic (1892) and Omphalopsychite (1882) "one of a body of monks who believed the deep contemplation of the navel induced communion with God," a derisive name given to the Hesychasts.