Subarachnoid refers to the space between the arachnoid and pia mater membranes that surround the brain and spinal cord. Synonyms for subarachnoid include meningeal, intrameningeal, perimeningeal, or subarachnoidal. These terms are often used interchangeably to describe conditions such as subarachnoid hemorrhage, which is bleeding that occurs in the subarachnoid space and can lead to serious brain damage. Other related terms include subdural, which refers to the space between the dura mater and arachnoid membranes, and epidural, which refers to the space between the skull and dura mater membranes. Understanding these different terms can help medical professionals effectively communicate with one another about neurological conditions and treatments.