Is there some rationale for this, or is this just Wanikani being sloppy? If they haven’t vetted their answers for synonyms, this is not out of beta.
Add it as a synonym if you want to. The word also has about 12 other meanings you could add if you want as well. WK doesn’t have every single applicable word or meaning for each entry.
Do I need a script or addon for that? I don’t see anything on the GUI to add a synonym.
Open an item after you review it or just go to the item page and click add synonym under the current meanings.
Click on the item, and in the meaning section there is “add synonym”