Webster's 1913 Dictionary
ARACHNIDA
A *rach "ni *da, n. pl. Etym: [NL. , fr. Gr. (Zoöl.)
Defn: One of the classes of Arthropoda. See Illustration in Appendix.
Note: They have four pairs of legs, no antennæ nor wings, a pair of mandibles, and one pair of maxillæ or palpi. The head is usually consolidated with the thorax. The respiration is either by trancheæ or by pulmonary sacs, or by both. The class includes three principal orders: Araneina, or spiders; Arthrogastra, including scorpions, etc. ; and Acarina, or mites and ticks.
ARACHNIDAN
A *rach "ni *dan, n. Etym: [Gr. (Zoöl.)
Defn: One of the Arachnida.
New American Oxford Dictionary
Arachnida
A rach ni da |əˈraknidə əˈræknɪdə |Zoology a class of chelicerate arthropods that includes spiders, scorpions, mites, and ticks. They have become adapted for a terrestrial life and possess book lungs and tracheae, and many have silk or poison glands. ORIGIN modern Latin (plural ), from Greek arakhnē ‘spider. ’
Oxford Dictionary
Arachnida
Arachnida |əˈraknɪdə | ▶plural noun Zoology a class of chelicerate arthropods that includes spiders, scorpions, mites, and ticks. They have become adapted for a terrestrial life and possess both lungs and tracheae, and many have silk or poison glands. ORIGIN modern Latin (plural ), from Greek arakhnē ‘spider ’.
The Wordsmith Dictionary