Main Entry: Arach·ni·da

Pronunciation: \ə-ˈrak-nəd-ə\

Function: noun plural

: a large class of arthropods that are mostly air-breathing by means of trachea or book lungs, that include the spiders and scorpions, mites, and ticks, and that have a segmented body divided into two regions of which the anterior bears four pairs of legs but no antennae

—arach·nid \-nəd\ adjective or noun