Something specious looks right but is not. A specious argument sounds reasonable, holds together while you listen to it, and yet is false when you check it. The whole force of the word sits in that gap between how it appears and what it is.

The most common phrases are specious argument, specious reasoning, and specious claim. It is used almost entirely about ideas, arguments, and explanations — not about people and not about objects. You would not call a fake bag specious.

It is stronger than simply 'wrong'. Calling an argument specious says that it is wrong AND that its wrongness is hidden behind a convincing surface — it is the sort of thing that fools people. Whether the speaker meant to fool anyone is left open, which is part of why writers like it: you can call the argument bad without directly calling the person a liar. Still, it is a sharp, critical word, and in speech it lands as a serious accusation.

This is a formal, written word — you meet it in editorials, philosophy, law, and academic writing, very rarely in conversation.

One historical note that makes it easier to remember: the old meaning of specious was simply 'good-looking, pleasing to the eye', from Latin speciosus. Over time the sense of 'only on the surface' took over and the word turned negative. Its ancestor is the Latin idea of look and appearance — which is the whole word in one image.