Which word describes a medical instrument used for examination of cavities?

The term that best describes a medical instrument used for the examination of cavities is endoscope. An endoscope is specifically designed to access and visualize internal cavities and organs, such as the gastrointestinal tract, lungs, or other hollow structures within the body. It is equipped with a camera and a light, allowing healthcare professionals to diagnose conditions, perform procedures, and even obtain tissue samples from inside these cavities.

The other options, while related to medical practices, do not serve the primary purpose of examining cavities in the same way. A probe is usually used for probing or testing and may not have the capability to visualize. A syringe is employed to inject or withdraw fluids rather than examine cavities. A scanner, such as a CT or MRI scanner, is useful for imaging structures but does not directly provide the interactive examination as an endoscope does.