adjective

Like a spider or arachnid.

intelligent arachnoid killing machines

noun

A fine, delicate membrane, the middle one of the three membranes or meninges that surround the brain and spinal cord, situated between the dura mater and the pia mater.

Between the pia and arachnoid membranes is the subarachnoid space, in which the cerebrospinal fluid circulates.