• (a.) Pertaining to the arachnoid membrane; arachnoid.
Ar`ach·noid'al adjective (Anat.) Pertaining to the arachnoid membrane; arachnoid. 
Type: Term Pronunciation: ar′ak-noy′dăl Definitions: 1. Relating to the arachnoid membrane, or arachnoidea.
arachnoidea, arachnoidal The middle of the three layers of the meninges covering the brain and spinal cord. Its smooth external sukrface is closely applied to the dukra mater, while the inner roughened surface is separated from the pia mater by the subarachnoid space. In some locations the space is crossed by fine trabeculae.