adjective
Definition: Describing something that is associated with a fraud or a person who pretends to have medical skills without proper qualifications.
Example: The doctor was known for his quack treatments that promised miraculous results.
intransitive verb
Definition: To make the sound that ducks make, which is a short, sharp noise.
Example: The ducks quack loudly every morning at the pond.
noun
Definition: A person who pretends to be a doctor or has medical skills but is not qualified; often used to describe someone who gives false medical advice.
Example: The town was warned about the quack who was offering fake treatments.