It's often used in medical and biological terms, indicating a connection or articulation.
Here are some examples:
* Arthritis: Inflammation of a joint.
* Arthropod: An invertebrate animal with jointed legs (like insects, spiders, and crustaceans).
* Arthroplasty: Surgical reconstruction or replacement of a joint.
* Arthroscope: A medical instrument used to examine the inside of a joint.
The prefix "arth" is a helpful indicator that the word relates to joints or the structure of joints.