- obpyriform
- Obrecht
- Obregón
- Obrenović
- Obrenovich
- obreption
- OBrit
- obrogation
- obs
- obs.
- obscene
- obscenity
- obscurant
- obscurantism
- obscuration
- obscure
- obscurely
- obscurity
- obscurum per obscurius
- obsecrate
- obsequence
- obsequent
- obsequent stream
- obsequies
- obsequious
- obsequiousness
- obsequy
- observable
- observance
- observant
- observation
- observational
- observation car
- observation post
- observative
- observatory
- observe
- observer
- obsess
- obsessed
- obsession
- obsessive
- obsessive-compulsive
- obsessive-compulsive disorder
- obsessively
- obsidian
- obsidian dating
- obsidianite
- obsidional coin
- obsolesc.
- obsolesce
- obsolescence
- obsolescent
- obsolete
- obstacle
- obstacle course
- obstacle race
- obstet.
- obstetric
- obstetrician
- obstetrics
- obstinacy
- obstinate
- obstipation
- obstreperous
- obstruct
- obstruction
- obstructionism
- obstructionist
- obstructive
- obstruent
- obtain
- obtaining by deception
- obtect
- obtemper
- obtest
- obtrude
- obtrusion
- obtrusive
- obtund
- obtunded
- obturate
- obtuse
- obtuse angle
- obtuseness
- obtuse triangle
- Obuda
- OBulg.
- obumbrant
- obumbrate
- obv
- obverse
- obversion
- obvert
- obviate
- obvious
- obviously
- obvolute
- Obwalden
- obˈserver
- OC
- oc-
- Oc.
- oca
- Ocala
- OCAM
- O Canada
- ocarina
- occ.
- Occam
- Occam's razor
- occas.
- occasion
- occasional
- occasionalism
- occasional licence
- occasionally
- occasional table
- occasions
- occident
- Occident
- occidental
- Occidentalism
- Occidentalize
- occipital
- occipital bone
- occipital condyle
- occipital lobe
- occiput
- Occitan
- Occleve
- occlude
- occluded front
- occlusion
- occlusive
- occult
- occultation
- occult balance
- occulting light
- occultism
- occultist
- occupancy
- occupant
- occupation
- occupational
- occupational disease
- occupational hazard
- occupational medicine
- occupational pension
- occupational psychology
- Occupational Safety and Health Administration
- occupational therapy
- occupation franchise
- occupation groupings
- occupation layer
- occupied
- Occupied Territories
- occupier
- occupy
- occur
- occurred
- occurrence
- occurrent
- occur to one
- occy
- OCD
- OCDM
- ocean
- oceanarium
- oceanaut
- Ocean City
- ocean engineering
- ocean floor spreading
- oceanfront
- oceangoing
- ocean-going
- ocean greyhound
- Oceania
- oceanic
- Oceanic
- oceanic crust
- oceanicity
- oceanic ridge
- oceanic trench
- Oceanid
- ocean liner
- ocean marine insurance
- Ocean of Storms
- oceanog.
- oceanographer
- oceanography
- oceanologic
- oceanology
- ocean pout
- Oceanside
- Ocean Springs
- ocean sunfish
- Oceanus
- Oceanus Procellarum
- ocellar
- ocellated
- ocellated turkey
- ocellation
- ocellus
- ocelot
- och
- oche
- ocher
- ochlesis
- ochlocracy
- ochlophobia
- Ochoa
- ochone
- Ocho Rios
- Ochozath
- Ochozias
- ochratoxin
- ochre
- ochrea
- ochroid
- Ochs
- ocicat
- Ockeghem
- ocker
- Ockham
- Ockham, William of
- Ockham's razor
- ockodols
- Ocmulgee
- oconee-bells
- ocotillo
- OCR
- Ocracoke Island
- ocrea
- ocreate
- OCS
- Oct
- oct-
- oct.
- Oct.
- octa
- octa-
- octachord
- octad
- octadecanoic acid
- octagon
- octagonal
- octagon house
- octagon scale
- octahedral
- octahedrite
- octahedron
- octal
- octal notation
- octamer
- octamerous
- octameter
- octan
- octandrious
- octane
- octanedioic acid
- octane number
- octangle
- octangular
- octanoic acid
- Octans
- octant
- octarchy
- octaroon
- octastyle
- octateuch
- octavalent
- octave
- octave coupler
- Octavia
- Octavian
- Octavius
- octavo
- octavus
- octennial
- octet
- octillion
- octo-
- October
- October Revolution
- Octobrist
- octocentenary
- octodecillion
- octodecimo
- octofoil
- octogenarian
- octomerous
- octometer
- octonary
- octopod
- octopus
- octoroon
- octosyllabic
- octosyllable
- octothorpe
