The following categories exist on the wiki, and may or may not be unused. Also see wanted categories.
- CIMAC (1 member)
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- COVID-19 (2 members)
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- Call centres (3 members)
- Cameras (1 member)
- Cannabis (1 member)
- Cardiagnostics.be (3 members)
- Carpets and rugs (1 member)
- Categories (1 member)
- Cedefop (1 member)
- Cement (1 member)
- ChatGPT (1 member)
- Chemical elements (1 member)
- Chemistry (4 members)
- Chris P. Odijk (1 member)
- Cito (1 member)
- Civil Engineering (1 member)
- Cleanrooms (1 member)
- Coastal engineering (1 member)
- Combustion engines (1 member)
- Concordancers (2 members)
- Construction (11 members)
- Crime (1 member)
- Crossword puzzles (1 member)
- Crypto (3 members)
- Czech (1 member)
- DSL (5 members)
- Danish (1 member)
- Diamonds (2 members)
- Dictation (2 members)
- Dictionaries (6 members)
- Digitising (0 members)
- Dikke Van Dale (1 member)
- Dokmar (1 member)
- Dragon (1 member)
- Dredging (1 member)
- Dunglish (2 members)
- Dutch (10 members)
- Dutch-English dictionaries (4 members)
- Dutch.AGROVOC (1 member)
- Dutch language (1 member)
- Dutchcadillac.nl (1 member)
- E-numbers (1 member)
- EENI Global Business School (1 member)
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- ESCO classification (2 members)
- EU (2 members)
- EUROPUMP (1 member)
- EY (1 member)