| ob | against |  | ob-, o-, oc-, of-, og-, op-, os-[126] | | ob | obduracy, obdurate, obduration, obfuscate, oblique, obliquity, obstinate, obstreperous, occur, offend, omit, oppose, ostensible, ostentatious |
| octogeni | eighty each |  | octogen- | | octogeni | octogenarian, octogenary |
| octogesimus | eightieth |  | octogesim- | | octogesimus | octogesimal |
| octoni | eight each |  | octon- | | octoni | octonary |
| octāvus | eighth |  | octav- | | octāvus | octaval |
| octō | eight | | oct- | | octō | octangular, octennial, octovir |
| oculus | eye |  | ocul- | | oculus, oculare | ocular, oculus, ullage |
| odium | hate |  | odi- | | odium | odious |
| odor | fragrant |  | odor- | | odor | malodorous, odoriferous, odorous |
| oleum | oil |  | ole- | | oleum | oleosity |
| oliva | olive |  | oliv- | | oliva | olivaceous, olivary, olivette |
| omasum | paunch |  | omas- | | omasum | abomasum, omasum |
| omentum | fat skin |  | oment- | | omentum | omental |
| omen | creepy |  | omin- | | omen, ominis | abominable, ominous |
| omnis | all |  | omni- | | omnis | omnipotence, omnipresent, omniscient, omnivore |
| onus | burden, load |  | oner- | | onus, oneris | exonerate, exoneration, onerous, onus |
| opacus | shady |  | opac- | | opacus | opacity, opacus, opaque |
| operire | cover |  | oper- | | operire, operculum | interoperculum, kerchief, opercular, operculiform, operculum |
| optare | choose |  | opt- | | optare | adopt, adoptee, adoption, adoptive, co-option, coopt, cooptation, nonoptional, opt, optation, optative, option, optional, optionality |
| optimus | best |  | optim- | | optimus | optimal, optimum |
| opus | work |  | oper- | | opus, operis | cooperate, inoperable, opera, operate, opus |
| orare | pray, plead |  | ora- | | orare “to pray, plead” | adore, adoration, exorable, inexorable, oracle, orate, oration, orator, oratorio, oratory, orison, perorate, peroration, perorator |
| orbis | circle |  | orb- | | orbis | orbit |
| oriri | rise |  | ori-, ort- | | oriri, ortus | aboriginal, abort, abortifacient, abortion, abortive, disorient, disorientation, orient, oriental, Orientalia, orientate, orientation, orientational, orientative, origin, original, originality, originate, origination, originator, reorient, reorientation |
| oscillum | swing |  | oscill- | | oscillum | oscillate, oscillation, oscillator, oscillatory |
| ostium | entrance |  | osti- | | ostium | ostiary, ostiolar, ostiole, ostium |
| os | bone |  | oss- | | os, ossis | exossation, interosseous, ossature, osselet, osseocartilaginous, osseointegration, osseous, ossicle, ossicular, ossiferous, ossification, ossifrage, ossify, ossuary |
| os | mouth |  | or- | | os (genitive oris) “mouth” | adosculation, inosculate, inosculation, interosculate, intraoral, oral, orifice, osculant, osculum, peroral |
| ovum | egg |  | ov- | | ovum | obovate, oval, ovarian, ovariole, ovary, ovate, ovicapsule, ovicidal, ovicide, oviduct, oviferous, oviform, oviposition, ovipositor, ovolo, ovular, ovulation, ovulatory, ovule, ovum, pluriovulate |
| ōrdō | order |  | ordin- | | ōrdō, ordinis | coordinal, coordinate, coordination, coordinator, disorder, extraordinaire, extraordinary, grandorder, incoordinate, incoordination, infraorder, inordinate, inordination, insubordinate, insubordination, magnorder, mirorder, ordain, ordainment, order, ordinal, ordinance, ordinand, ordinariate, ordinary, ordinate, ordination, ordinative, ordnance, ornery, parvorder, preordain, preorder, preordination, quasiorder, reordain, reorder, reordination, suborder, subordinary, subordinate, subordination, superordain, superorder, superordinate, superordination |
| ōrnāre | decorate |  | orn- | | ōrnāre | adorn, adornment, ornament, ornamental, ornamentation, ornate, ornative, ornature, suborn, subornation |
