An EYER is a four-letter term for someone who observes. This person is likely to be looking out for something specific, such as a particular type of behavior or activity. A noter is a five-letter term for someone who also observes, but this person is likely to be taking notes or recording information about what they are seeing. Finally, a spier is a five-letter term for someone who observes in a more secretive manner, often gathering information without being noticed. All three terms refer to someone who is paying attention to their surroundings and taking note of what is happening.