Ne-go-ti-a-tion, negeseuaeth; cyflafaredd
No-to-ri-e-ty, hynodrwydd; erchylldra
O-bit-u-a-ry, marwrestr
Ob-serv-a-to-ry, tremynfa, arsyllfa
Op-por-tu-ni-ty, amser, cyfleusdra, adeg
Or-gan-i-za-tion, iawnffurfiad, iawnosodiad
Pa-ci-fi-ca-tion, heddychiad; dyhuddiad
Par-si-mo-ni-ous, cynnil, arbedus, cybyddlyd
Pe-ri-od-i-cal, cylchawl, cylchynawl
Per-pen-dic-u-lar, unionsyth, unionseth