A.A. - Acto
- A.A.
- A.B.
- A.B.A.
- A.C.
- a.d.
- A.D.
- A.M.
- A.M.D.G.
- A.Q.I.C.
- A.R.S.
- A.U.
- Aachen
- Aarhus, Ancient See of
- Aaron
- Ab.
- Abachum, Audifax, Martha, and Maris, Saints
- Abaddon
- Abandonment
- Abarca, Pedro
- Abarim
- Abba
- Abbacy Nullius of Wettingen-Mehrerau
- Abbadie, Antoine d'
- Abban of Magheranoidhe, Saint
- Abban of New Ross, Saint
- Abban the Hermit, Saint
- Abbate Giuseppe Baini
- Abbé
- Abbeloos, Jean Baptiste
- Abbess
- Abbey
- Abbey and Congregation of Melk
- Abbey and Diocese of Bobbio
- Abbey and School of Clonmacnoise
- Abbey of Arbroath
- Abbey of Bec
- Abbey of Benedictbeurn
- Abbey of Citeaux
- Abbey of Clairvaux
- Abbey of Cornillon