Ob-struct, attal, rhwystro
Ob-tain, cael, caffael, cyrhaeddyd
Ob-trude, ymwthio; trawsgymmell
Oc-cult, cuddiedig, dirgel
Oc-cur, dygwydd; dyfod i gof
O-cean, cefnfor, yr eigion
O-dour, arogl, sawyr
Of-fals, syrth; gweddillion
Of-fence, camwedd, trosedd; tramgwydd
Of-fend, troseddu; tramgwyddo