Definitions for arachnida
Arachnida, class Arachnida(noun)
a large class of arthropods including spiders and ticks and scorpions and daddy longlegs; have four pairs of walking legs and no wings
one of the classes of Arthropoda. See Illustration in Appendix
U.S. National Library of Medicine
A class of Arthropoda that includes SPIDERS; TICKS; MITES; and SCORPIONS.