544 abbreviations
NN.Nostris ("To Our" with a plural) or Numeri ("Numbers")
No.Nobis ("to us", "for us")
Nob.Nobilis, Nobiles ("Noble", "Nobles")
Noct.Nocturnum ("Nocturn")
Non.Nonae ("Nones")
Nostr.Noster, nostri ("Our", "of our")
Not.Notitia ("Knowledge")
N.S.Notre Seigneur, Nostro Signore ("Our Lord")
N.S.New Style
N.T.Novum Testamentum ("New Testament")
Ntri.Nostri ("Of our")
Nultus.Nullatenus ("Nowise")
Nup.Nuptiae ("Nuptials")
O.Hora ("Hour"); Obiit ("Died")
Ob.Obiit ("Died")
OB. IN XTO.Obiit In Christo ("Died In Christ")
O.C.Ordo C(h)aritatis (Fathers of the Order of Charity)
O. Camald.Ordo Camaldulensium (Camaldolese)
O. Cart.Ordo Cartusiensis (Carthusians)
O.C.C.Ordo Carmelitarum Calceatorum (Carmelites)
O.C.D.Ordo Carmelitarum Discalceatorum (Discalced, or Barefoot, Carmelites)
O. Cist.Ordo Cisterciensium (Cistercians)
O.C.R.Ordo Reformatorum Cisterciensium (Cistercians, Trappists)
Oct.Octava ("Octave" Breviary)
O.F.M.Ordo Fratrum Minorum (Observant Franciscans)
O.M.Ordo [Fratrum] Minimorum (Minims of St. Francis of Paola)
O.M.C.Ordo Minorum Conventualium (Conventual Franciscans)
O.M. Cap., O.F.M. Cap., O.M.C.Ordo Minorum Cappucinorum (Capuchins)
O. Merced.Ordo Beatae Mariae Virginis de Redemptione Captivorum (Mercedarians, Nolaschi)
O.M.I.Oblati Mariae Immaculatae (Oblate Fathers of Mary Immaculate)
Omn.Omnes, Omnibus ("All", "to all")
OMS.Omnes ("All")
OP.Optimus (Excellent, or Supremely Good)
O.P., Ord. Fratr. Praed.Ordo Praedicatorum (Dominicans)
Op. Cit.Opere Citato ("In the work cited")
Or.Oratio ("Prayer" Breviary)
Ord.Ordo, Ordinatio, Ordinarius ("Order", "Ordination", "Ordinary")
Ordinaoni.Ordinationi ("Ordination" dat. case)
Ordio.Ordinario ("Ordinary" dat. or abl. case)
Ord. Praem.Ordo Praemonstratensium (Premonstratensians, Norbertines)
Or. Orat.Orator ("Petitioner"), Oratorium ("Oratory")
O.S.Old Style
O.S.A.Ordo [Eremitarum] Sancti Augustini (Augustinians)
O.S.B.Ordo Sancti Benedicti (Benedictines)
O.S.C.Oblati Sancti Caroli (Oblate Fathers of St. Charles)
O.S.F.C.Ordinis Sancti Francisci Capuccini (Franciscan Capuchins)
O.S.F.S.Oblati Sancti Francisci Salesii (Oblate Fathers of St. Francis of Sales)
O.S.H.Ordo [Eremitarum] Sancti Hieronymi (Hieronymites)
O.S.M.Ordo Servorum Mariae (Servites)
O.SS.C.Oblati Sacratissimi Cordis ("Oblate Fathers of the Sacred Heart")