A stirrer can refer to different things depending on the context. Here are some possible definitions based on the search results:

• Implement for stirring: A stirrer can be an implement or device used for stirring something, such as a magnetic stirrer in a laboratory. It can also refer to a stirring rod or spoon used in cooking.

• Person who causes trouble: In British and Australian English, a stirrer can be a person who deliberately causes trouble or tries to create conflict between others. This usage is informal and often carries a negative connotation.

In summary, a stirrer can be a tool for stirring liquids or a person who stirs up trouble.