Op-pon-ent, gwrthwynebwr; gwrthwynebol
Op-por-tune, prydlawn; addas
Op-po-site, gwrthwyneb; cyferbyn
Op-pres-sion, gorthrymder, gormes
Op-pres-sive, gorthrymus, treisiawl
Op-pres-sor, gorthyrmwr, gormeswr
Op-ta-tive, dymunedigol; dymunadwy
Op-u-lence, cyfoeth, golud
Op-u-lent, cyfoethog, goludog
Or-a-cle, arma; gwr doeth