- oasis
- object art
- object photography
- object study (subject / genre)
- oboe
- occupation (war)
- occupational health and safety
- Occupational therapy
- Oceania (culture area)
- oceanology
- offer / quote (sale)
- Office / Administration (Commercial Sector)
- office clerk
- Office Furniture /Office Furnishings
- office machine
- office supplies (misc.) (equipment / tools)
- office supplies / stationery
- offset printing
- oil
- Oil Can
- oil industry / oil production
- old age
- oliphant
- olympiad
- olympic games / olympics
- Oncology
- Onion Chopper
- online-marketing / online-advertising
- op art
- Op-ed article (journalism)
- open house
- open-air event / open-air concert
- opening hours (sale)
- opera
- operating manual / instruction manual
- operating system
- operation of a vehicle / driving
- ophthalmology
- opposite (logic)
- optical illusion
- optics
- orchestra (ensemble)
- Orchestral work
- orchestration
- Orderliness / Tidying (Housekeeping)
- organ (musical instrument)
- organic food
- organised crime
- organizational form / legal structure (company)
- oriel
- orientalism
- orienteering
- origami
- original (product feature)
- ornament (subject)
- ornamental plant (misc.)
- orthography
- orthopedics
- outdoor advertising
- Outdoor Furniture / Garden Furniture
- outline / silhouette (subject / genre)
- output device
- outsider
- outsider art
- outwork
- Oven
- Overall (Arbeitskleidung)
- overshoe