Akademik
Opus - Pall
Opus Anglicanum
Opus Dei
Or
Ora
Oratores
Oratory
Ordainers
Ordeal, trial by
Ordinances of 1311
Ordinary
Ordo equestris
Oriflamme
Original writ
Originalia Rolls
Orillion
Orphrey
Orpiment
Ostiarius
Ostium ecclesiae
Ostmen
Outlaw
Outremer
Overslop
Overt
Ox
Oxford, Provincial Synod of
Oxford, Provisions of
Oxford, University of
Oxgang
Oyer and determiner
Page
Paint
Palatinate
Palatine
Pale
Palet
Palfrey
Palimpsest
Palisade