The following categories exist on the wiki, and may or may not be unused. Also see wanted categories.
- Obsidian (1 member)
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- Onroerend Goed Lexicon (4 members)
- Oosthoek (1 member)
- Open Dutch WordNet (ODWN) (3 members)
- Ophthalmology (1 member)
- Ordinal numerals (1 member)
- Origin unknown (10 members)
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- Oxford University Press (OUP) (1 member)
- Oxforddictionaries.com (1 member)
- P&ID (1 member)
- PIANC (2 members)
- PR (2 members)
- PRINCE2 (1 member)
- Pages using Tabber parser tag (0 members)
- Pages with broken file links (50 members)
- Palletising (7 members)
- Paper copy (1 member)
- Paper industry (1 member)
- PatTR (1 member)
- Patentese (1 member)
- Patents (18 members)
- Patitia.net (1 member)
- Pegasus (1 member)
- Peter Kutschera (1 member)
- Piracy (1 member)
- Plants (2 members)
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- Proz.com (3 members)
- Public procurement (1 member)
- Pumps (5 members)
- Puzzelwoordenboek (27 members)
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- R-Phrases (2 members)
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