quack

The word "quack" has two main meanings, and they are quite far apart. The first is simple and easy to hear: it is the sound a duck makes. In this sense, it can be a noun or a verb. You might say, "We heard a quack from the lake," or "The ducks were quacking all morning." This is the basic, everyday meaning, and it comes from imitation of the sound itself.

The second meaning is negative. A quack is someone who falsely claims medical knowledge or pretends to be able to cure people. This often suggests dishonesty, not just ignorance. You may see it in phrases like quack doctor or in warnings about fake health cures. In this sense, the word is not a neutral label; it is a strong criticism.

You may sometimes find the word used more loosely for a dishonest person who acts like an expert in health or healing, even without being an actual doctor. But that medical idea stays at the center of the meaning. So when you see "quack," think either of a duck's familiar call or of a fake medical professional making claims that should not be trusted.