arachno-, arachn- +

(Greek: spider; the arachnoidea; when used in medicine this Greek element refers to a membrane, veins, or any web-like structure in the body)

arachnactis (s) (noun), arachnactines (pl)
A planktonic larva of tube anemones or the order Ceriantharia: Sally read about arachnactines in her biology book and found out that they are free-swimming larva of particular actinians.
Arachne (proper noun)
Despite the generally adverse feelings of many people towards spiders, they have in many parts of the world become a part of folk myth and legend, perhaps more so than any other anthropod.

The very name Arachnida, the arthropod class to which the spiders belong, is derived from the story of the Greek maiden from Lydia, Arachne, who was so skilled as a weaver that she had the audacity to challenge the goddess Athena to a weaving contest.

Athena accepted the challenge and wove a tapestry depicting the majesty of the gods while Arachne wove one depicting the gods' amorous adventures or love affairs.

Enraged at the perfection of her rival's work, Athena tore it to shreds, which so upset the maiden that she hanged herself. Out of pity, Athena is said to have loosened the rope from around Arachne's neck which was turned into a cobweb, and Arachne was changed into a spider, doomed to spend the rest of her life weaving.

Spiders of the World by Rod & Ken Preston-Mafham;
Facts On File Publication; New York; 1984; page 14.
arachnean (adjective) (not comparable)
Resembling a spider's web: Mary was told by her mother that the fabric of her dress was of an arachnean quality possessing a lightness and being very fine in texture.
arachnid (s) (noun), arachnids (pl)
A member of Arachnida, a class of arthropods, including scorpions, spiders, ticks, and mites: Arachnids are distinguished from insects by having four pairs of walking legs and by having the head and thorax in a single prosoma.

Arachnida (proper noun)
A class of arthropods of the subphylum Chelicerata, that includes mites, ticks, spiders, scorpions, and related forms: Many of the most important parasites and vectors of human and animal pathogens are included in this large assemblage termed Arachnida.

More about Arthropoda

Along with the insects, crustaceans, centipedes, and millipedes; spiders are members of that group of animals without backbones referred to as the Arthropoda, literally the "jointed-limbed" animals.

Clearly they lack a backbone and instead have an external skeleton, called an "exoskeleton", which has some similarities to a suit of armor; it is tough and fairly rigid and the muscles are attached to it internally.

Like the vertebrate skeleton, that of the arthopods is designed as a compromise between rigidity, to provide support and protection for the soft, delicate internal organs, and flexibility, to allow for ease of movement.

Spiders of the World by Rod & Ken Preston-Mafham;
Facts On File Publication; New York; 1984; page 16.
arachnidan (s) (noun), arachnidans (pl)
Any of various arthropods of the class Arachnida: Spiders, scorpions, mites, and ticks are all arachnidans, and are characterized by four pairs of segmented legs and a body that is divided into two regions, the cephalothorax and the abdomen.
arachnidial (adjective) (not comparable)
Pertaining to the Arachnida: The arachnidial creatures that were crawling along on the sand were scorpions, and so Jane thought it best to avoid them!
arachnidian (adjective) (not comparable)
Relating to, or resembling, a member of the class Arachnida: The arachnidian creature Mark saw on the wooden fence seemed to be a garden spider with eight legs!
arachnidism (s) (noun) (no pl)
A morbid condition resulting from the bite of an arachnid: Arachnidism may include an ascending motor paralysis and a destruction of peripheral nerve endings.

Arachnidism is also called "spider poisoning", "arachnoidism", and "araneism".

arachnidium (s) (noun), arachnidia (pl)
The glandular organ in which the material for the web of spiders is secreted: The arachnidium is the spinning apparatus of a spider, including the spinning glands and spinnerets.
arachnidologist (s) (noun), arachnidologists (pl)
Someone who specializes in the study of spiders: Susan's mother wanted to become an arachnidologist and become an expert in arachnids, including not only spiders, but also ticks, scorpions, mites and harvestmen.
arachnidology (s) (noun), arachnidologies (pl)
A branch of zoology that is concerned with arachnids: Since John was fascinated by scorpions and spiders, he decided to study arachnidology after finishing school!
arachnidous (adjective) (not comparable)
Of the nature of the Arachnid: Dr. Thompson was surprised at the arachnidous infection that Arthur had on his leg, evidently from having been bitten by a tick.
arachniform (adjective), more arachniform, most arachniform
Resembling, or in the form of, a spider web: The finely and delicately crocheted corner of the handkerchief had an arachniform appearance.

The most striking physical properties of spider silk are its strength and elasticity. It has been found that a thread .01 centimetre in diameter will support a weight of 80 grammes before breaking, and will stretch by over twenty per cent of its original length.

—Keith C. McKeown; Spider Wonders of Australia;
Halstead Printing; Sydney, Australia; 1936; page 218.
arachnitis (s) (noun) (no pl)
Inflammation of the arachnoid membrane: Arachnitis is a neuropathic disease causing a redness, swelling, and painfulness when the membrane protecting the brain and spinal cord is infected.

Cross references of word families that are related directly, or indirectly, to: "spider; arachnoidea": acaro-; arano-; mite, mites.