I have, with slight reservations, made dictionaries the master tag in this merge, for several reasons:
- dictionaries has been favored over dictionary by a factor of 8.
- Unlike, say, indefinite-article, there are many dictionaries in the English-speaking world.
- Existing questions rarely seem to ask about a specific dictionary; rather, they ask about either multiple dictionaries or dictionaries in general.
- We traditionally favor the plural form of a tag in any case.
- @kiamlaluno's argument is not extremely persuasive. If I have multiple dictionaries, but I'm not referring to any in particular, I might use the singular. But if I want to consult all of them, I would probably use the plural.
Nonetheless, I'm open to reversing the synonym if there is a good reason.