The following categories exist on the wiki, and may or may not be unused. Also see wanted categories.
- Transport (2 members)
- Two-letter language codes (1 member)
- UCTE (1 member)
- UIC (1 member)
- UK vs US English (1 member)
- ULTRAMARIN.online (1 member)
- USPTO (1 member)
- US vs UK English (1 member)
- Universiteit Antwerpen (1 member)
- Utrecht University (2 members)
- V&A (2 members)
- VCA (1 member)
- VERA (2 members)
- Van Dale (5 members)
- Van Houtum (1 member)
- Varkenspest (1 member)
- Villa Kogelhof (1 member)
- Vlaanderen (1 member)
- WILD BEEF (1 member)
- Water (3 members)
- Waterbouwkunde (1 member)
- Wayback Machine (1 member)
- Weaving (1 member)
- Webster’s (1 member)
- Weed (1 member)
- Wikidata (1 member)
- Wikipedia (18 members)
- Wikipedia glossaries (1 member)
- Wikipedia mirrors (1 member)
- Wiktionary (7 members)
- Wiktionary-dict (6 members)
- Wolters (1 member)
- WordNet (3 members)
- Ziekenhuis.nl (1 member)
- admin (9 members)
- back pulse (2 members)
- backwash (1 member)
- buttered sausage (1 member)
- encymed.com (1 member)
- geometric terms of location (1 member)
- iNDENT (1 member)
- m (1 member)
- piektraining.com (1 member)
- pollackassociates.com (1 member)
- quizlet.com (1 member)
- railAlert (2 members)
- ttmem.com (3 members)
- vena.be (1 member)
- warpedforgood.com (1 member)
- woordjesleren.nl (1 member)