The word "arachnoid" refers to something or someone that is related to spiders. It can be used to describe characteristics, parts, or even diseases associated with spiders or spider webs. Full definition
Under normal circumstances, there are multiple layers within the nose that block the access of pharmaceutical agents from getting to the brain including bone and the dura / arachnoid membrane, which represents part of the blood - brain barrier (B). (sciencedaily.com)
Syringomyelia can occur as a consequence of any alteration to the normal flow pattern of CSF such as arachnoid cysts / adhesions (Fig 5), malformations such as spina bifida and spinal dysraphism, tumors (Fig 6), inflammatory disease such as (in the cat) feline infectious peritonitis, and secondary to trauma. (caninechiariinstitute.org)
Then arrange them in floating «constellations,» with lengths of wire or string, resulting in arachnoid stabiles that climb walls or delicate hanging mobiles. (nytimes.com)