subcategories refers to lower level categories.
Which term should I use to refer to higher level categories?
supercategories sound right?
I don't think there's an antonym for "sub" since we use "sub" to talk about something which is a level down from something else. For example, "sub-category" is a category within a category. If you have to go further, you may use "sub-sub category." But in the end, the only category above all of these is simply a "category."
If you were to refer to the first category from which the "sub-category" and "sub-sub category" are taking birth, you may do so with "main category."
Hope I answered your question.
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