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(ă-rak′noyd") [Gr. arachnē, spider, spider web -oid] 1. Resembling a web. 2. Arachnoid membrane.

spinal a. Arachnoidea spinalis.


(ă-rak″noyd′ē-ă) [L. fr. Gr. arachnoeidēs] Arachnoid membrane.

a. encephali The part of the arachnoidea enclosing the brain. SYN: cranial arachnoid.

a. spinalis The part of the arachnoidea enclosing the spinal cord. SYN: spinal arachnoid.


(ă-rak′noyd″izm) [arachnoid + -ism] Arachnidism.


(ă-rak″noyd-īt′ĭs) [arachnoid + -itis] Inflammation of the arachnoid membrane. SYN: arachnitis.


(ă-rak″nō-lī′sĭn) [Gr. arachnē, spider, spider web + lysin] The hemolysin present in spider venom.


(ă-rak″nō-fō′bē-ă) [Gr. arachnē, spider, spider web + -phobia] A phobia of spiders.

Ara h2

A protein in peanuts that triggers allergic responses, including life-threatening immunoglobulin E-mediated anaphylaxis.

Aran-Duchenne disease

(ă-ran′dŭ-shĕn′) [F. A. Aran, Fr. physician, 1817–1861; G. B. A Duchenne, Fr. neurologist, 1807–1875] Spinal muscular atrophy.

Arantius, Julius Caesar

(ă-ran′shē-ŭs, ă-ran′tē-ŭs) Italian anatomist and physician, 1530–1589.


angiotensin II receptor blocker.


(ar-bi-trā′shŏn) [L. arbitratio, decision] 1. A legal procedure for settling a dispute outside the courts, in which the parties select and agree to abide by the decision of a neutral third party (the arbiter or arbitrator). 2. In radiology, the interpretation of images by two or more readers, who determine and report their findings after conferring together.


(ar′bŏr) [L. arbor, tree] A structure resembling a tree with branches.


(ar″bŏ-res′ĕnt) [L. arborescere, to grow into a tree] Branching out like a tree; treelike. SYN: dendriform; dendroid. arborescence (ar″bŏ-res′ĕns), n.


(ar″bŏ-rĭ-zā′shŏn) [arbor] Ramification or branching, esp. terminal branching of nerve fibers and capillaries. SEE: ferning; nerve.

arbor vitae

(ar′bŏr vīt′ē) [L. arbor vitae, tree of life] 1. A treelike structure or outline seen in a section of the cerebellum. 2. A tree or shrub of the genus Thuja or Thujopsis. 3. A series of branching ridges within the cervix of the uterus.


(ar″bŏ-vī′rŭs) [ar(thropod-) bo(rne) virus] Any of a large group of viruses that multiply in both vertebrates and arthropods such as mosquitoes and ticks. Arboviruses cause diseases such as yellow fever and viral encephalitis. SYN: arbor ...

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