- ocarina
- Occam
- occasion
- occasional
- Occident
- occidental
- occipital
- occlude
- occlusion
- occlusive
- occult
- occultism
- occultist
- occupancy
- occupant
- occupation
- occupational
- occupier
- occupy
- occur
- occurrence
- ocean
- oceanfront
- oceangoing
- Oceania
- oceanic
- oceanographer
- oceanographic
- oceanography
- oceanology
- Oceanside
- Oceanus
- ocelot
- och
- ocher
- Ochoa
- ocker
- OCR
- Oct
- octagon
- octagonal
- octahedral
- octahedron
- octal
- octane
- octant
- octave
- Octavia
- Octavian
- Octavio
- octavo
- octet
- octette
- October
- octogenarian
- octopus
- ocular
- oculist