[ ə'raknɔɪd ]
■ adjective like a spider or arachnid.
■ noun (also ~ membrane ) Anatomy the fine middle membrane of the three surrounding the brain and spinal cord, situated between the dura mater and the pia mater.
Origin
C18: from mod. L. ~es , from Gk arakhnoeidēs 'like a cobweb', from arakhnē 'spider'.