Something unarguable is so clearly true that there is nothing left to argue about. If you put it on the table, no reasonable person can push back. Facts are the usual case: "It is unarguable that prices have gone up." Notice what the word is really doing in a conversation, though. People rarely say it about something boring and obvious — nobody says "it is unarguable that water is wet". They say it when they are making a case, and they want to mark one particular point as settled so the discussion can move past it. So it often carries a small note of "stop arguing about this bit". That is why it sounds formal and slightly forceful; you meet it in writing, in speeches, in reports, much more than in chat with friends. In everyday speech Taiwanese students are far more likely to hear undeniable, or just "you can't argue with that". A quieter use is about a quality rather than a claim: "her unarguable talent" means talent nobody would dispute. Careful with the noun form, which some dictionaries also list — it is very rare, and you are safe treating this as an adjective.

無可爭辯的、無庸置疑的（口語會說「這點沒得吵」）。