| OAK | 16 | 5 |
| OAKHAM | 16 | 760 |
| OATES | 16 | 557 |
| OATHS | 16 | 1,968 |
| OBADIAH | 16 | 394 |
| OBAN | 16 | 192 |
| OBE | 16 | 227 |
| OBELISK | 16 | 193 |
| OBERLIN | 16 | 1,043 |
| OBERNAI | 16 | 65 |
| OBIDOS | 16 | 841 |
| OBLATE | 16 | 44 |
| OBLIQUE | 16 | 26 |
| OBLONG | 16 | 24 |
| OBOJAN | 16 | 58 |
| OBY | 16 | 63 |
| OCANA | 16 | 169 |
| OCCAM | 16 | 379 |
| OCCULTATION | 16 | 23 |
| OCCUPANCY | 16 | 57 |
| OCEANUS | 16 | 87 |
| OCELLUS LUCANUS | 16 | 551 |
| OCHIL HILLS | 16 | 90 |
| OCKLEY | 16 | 151 |
| OCLISEER | 16 | 33 |
| O'CONNELL | 16 | 2,241 |
| OCTAGON | 16 | 5 |
| OCTAHEDRON | 16 | 17 |
| OCTAVIA | 16 | 621 |
| OCTOBER | 16 | 105 |
| ODE | 16 | 477 |
| ODER | 16 | 132 |
| ODESSA | 16 | 1,279 |
| ODIHAM | 16 | 82 |
| ODIN | 16 | 9 |
| ODOACER | 16 | 48 |
| ODONTOLOGY | 16 | 95,324 |
| ODRYSE | 16 | 902 |
| OEDENBURG | 16 | 811 |
| OEHLENSCHLAGER | 16 | 2,960 |
| OELS | 16 | 304 |
| OERSTED | 16 | 9 |
| OESSEL | 16 | 269 |
| OETINGER | 16 | 140 |
| OFANTO | 16 | 60 |
| OFFENBACH | 16 | 582 |
| OHIO | 16 | 3,720 |
| OHLAU | 16 | 115 |
| OICH | 16 | 54 |
| OILS | 16 | 7,841 |
| OISE | 16 | 706 |
| OKA | 16 | 110 |
| OKAMANDAL | 16 | 212 |
| O'KEEFFE | 16 | 364 |
| OKEN | 16 | 5,700 |
| OKHOTSK | 16 | 466 |
| OLDCASTLE | 16 | 587 |
| OLDENBURG | 16 | 1,954 |
| OLDHAM | 16 | 1,608 |
| OLDYS | 16 | 181 |
| OLEARIUS | 16 | 333 |
| OLERON | 16 | 142 |
| OLINDA | 16 | 47 |
| OLIVA | 16 | 311 |
| OLIVAREZ | 16 | 472 |
| OLIVENZA | 16 | 66 |
| OLIVER | 16 | 205 |
| OLIVES | 16 | 232 |
| OLIVET | 16 | 352 |
| OLIVIER | 16 | 304 |
| OLMUTZ | 16 | 278 |
| OLNEY | 16 | 105 |
| OLONETZ | 16 | 711 |
| OLORON | 16 | 90 |
| OLOT | 16 | 423 |
| OLYMPIA | 16 | 661 |
| OLYMPIAS | 16 | 481 |
| OLYMPIC GAMES | 16 | 392 |
| OLYMPIODORUS | 16 | 389 |
| OLYMPUS | 16 | 294 |
| OLYNTHUS | 16 | 399 |
| OMAGH | 16 | 107 |
| OMAN | 16 | 35 |
| OMEN | 16 | 866 |
| OMEN LITERALLY | 16 | 830 |
| OMER | 16 | 262 |
| OMERCOTE | 16 | 66 |
| OMETEPE | 16 | 114 |
| OMSK | 16 | 126 |
| OMUN | 16 | 36 |
| ONATAS | 16 | 140 |
| ONDA | 16 | 61 |
| ONEGA | 16 | 196 |
| ONEGLIA | 16 | 111 |
| ONGOL | 16 | 75 |
| ONKELOS | 16 | 371 |
| ONOMATOPEIA | 16 | 55 |
| ONOSANDER | 16 | 155 |
| ONTENIENTE | 16 | 62 |
| ONTOLOGY | 16 | 27 |
| OOCHEYRA | 16 | 635 |
| OODEYPOR | 16 | 140 |
| OOJEIN | 16 | 348 |
| OOMRAWUTTEE | 16 | 110 |
| OORCHA | 16 | 176 |
| OORT | 16 | 160 |
| OOSTERHOUT | 16 | 52 |
| OOTAKAMUND | 16 | 98 |
| OPERA | 16 | 204 |
| OPHILOGY | 16 | 17 |
| OPHIR | 16 | 658 |
| OPIE | 16 | 886 |
| OPITZ | 16 | 231 |
| OPIUM | 16 | 1,487 |
| OPORTO | 16 | 1,570 |
| OPPELN | 16 | 235 |
| OPPELS | 16 | 70 |
| OPPIAN | 16 | 766 |
| OPPIDO | 16 | 67 |
| OPTICS | 16 | 203,466 |
| ORACLE | 16 | 1,393 |
| ORAN | 16 | 270 |
| ORANGE | 16 | 1,886 |
| ORCHOMENUS | 16 | 692 |
| ORDEAL | 16 | 1,295 |
| ORDERS | 16 | 192 |
| ORDERICUS | 16 | 517 |
| ORDINATION | 16 | 2,650 |
| ORDNANCE | 16 | 23 |
| ORES | 16 | 39 |
| OREBRO | 16 | 264 |
| OREGON | 16 | 1,990 |
| OREL | 16 | 484 |
| ORENBURG | 16 | 1,015 |
| ORESTES | 16 | 344 |
| ORFAH | 16 | 122 |
| ORFILA | 16 | 1,014 |
| ORFORD | 16 | 101 |
| ORGAN | 16 | 5,324 |
| ORGANO-LYRICON | 16 | 437 |
| ORIA | 16 | 103 |
| ORIBASIVS | 16 | 2,211 |
| ORIHUELA | 16 | 664 |
| ORINOCO | 16 | 1,066 |
| ORION | 16 | 310 |
| ORISSA | 16 | 458 |
| ORISTANO | 16 | 188 |
| ORIZABA | 16 | 97 |
| ORKNEY ISLANDS | 16 | 6,276 |
| ORLEANS | 16 | 1,163 |
| ORLEANS | 16 | 5 |
| ORLEY | 16 | 160 |
| ORLOFF | 16 | 539 |
| ORLOP | 16 | 19 |
| ORME | 16 | 368 |
| ORMEA | 16 | 63 |
| ORME'S HEAD | 16 | 46 |
| ORMOND | 16 | 5 |
| ORMSKIRK | 16 | 144 |
| ORMUZ | 16 | 405 |
| ORNE | 16 | 675 |
| ORNITHOLOGY | 16 | 121,009 |
| OWEN | 16 | 66 |
| OROBIO | 17 | 351 |
| ORONTES | 17 | 229 |
| OROSIUS | 17 | 1,685 |
| ORTHEZ | 17 | 296 |
| ORTHOGRAPHIC PROJECTION OF THE SPHERE | 17 | 42 |
| ORTONA | 17 | 190 |
| ORVIETO | 17 | 207 |
| OSAKA | 17 | 295 |
| OSCHATZ | 17 | 123 |
| OSCHOPHORIA | 17 | 189 |
| OSERO | 17 | 87 |
| OSIMO | 17 | 100 |
| OSIRIS | 17 | 12 |
| OSNABURG | 17 | 603 |
| OSORIO | 17 | 339 |
| OSSA | 17 | 76 |
| OSSIAN | 17 | 3,759 |
| OSSOLI | 17 | 1,094 |
| OSTADE | 17 | 294 |
| OSTASHKOV | 17 | 91 |
| OSTEND | 17 | 589 |
| OSTERODE | 17 | 87 |
| OSTERVALD | 17 | 357 |
| OSTIA | 17 | 290 |
| OSTRACISM | 17 | 1,317 |
| OSTROG | 17 | 62 |
| OSTROGOHSK | 17 | 58 |
| OSTROWO | 17 | 26 |
| OSTUNI | 17 | 33 |
| OSUNA | 17 | 277 |
| OSWEGO | 17 | 303 |
| OSWESTRY | 17 | 215 |
| OTAHEITE | 17 | 384 |
| OTHMAN | 17 | 239 |
| OTHO | 17 | 1,332 |
| OTLEY | 17 | 122 |
| OTRANTO | 17 | 5 |
| OTTAJANO | 17 | 46 |
| OTTAWA | 17 | 340 |
| OTTLEY | 17 | 161 |
| OTWAY | 17 | 1,548 |
| OUDE | 17 | 11,803 |
| OUDINOT | 17 | 311 |
| OUGHTRED | 17 | 54 |
| OUGLITSCH | 17 | 98 |
| OUNDLE | 17 | 104 |
| OURG | 17 | 67 |
| OURO PRETO | 17 | 150 |
| OUSE | 17 | 242 |
| OUTLAW | 17 | 1,890 |
| OVERTON | 17 | 5,854 |
| OWEN | 17 | 4,725 |
| OXENSTIERN | 17 | 355 |
| OXFORD | 17 | 3,021 |
| OXFORDSHIRE | 17 | 1,261 |
| OXUS | 17 | 329 |
| OYER AND TERMINER | 17 | 37 |
| OZANAM | 17 | 233 |
| OZELL | 17 | 180 |
| OZEROV | 17 | 203 |
| OZIERI | 17 | 469 |
| OUTLINES OF BOTANY | 18 | 216 |