Lewis & Short

2. commūnĭo, ōnis, f. [communis], a communion, mutual participation (several times in Cicero, elsewhere rare).

  1. I. In gen.: inter quos est communio legis, inter eos communio juris est, Cic. Leg. 1, 7, 23: sanguinis, id. Rosc. Am. 22, 63: litterarum et vocum, id. Tusc. 5, 2, 5: sermonis, * Suet. Aug. 74: parietum, Tac. A. 15, 43: victoriae, id. ib. 12, 19: temporum alicujus, Cic. Mil. 36, 100: beneficiorum, praemiorum civitatis, id. Balb. 12, 29: visorum, id. Ac. 2, 14, 44: plures partes communione complecti, id. de Or. 1, 42, 189: in pristinā communione manere, id. ib. 3, 19, 72: sagariam communionem inire, Dig. 17, 2, 52.
  2. II. In eccl. Lat.
    1. A. Church communion, Sulp. Sev. Hist. Sacr. 2, 45; 2, 37; Aug. in Ps. 57, n. 15.
      Hence,
    2. B. The sacrament of the Lord’s supper, communion: sancti altaris, Aug. Ep. 54, 6.