n pl :  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 adj or n 
 
 
 
Similar sounding terms:   arachnoid  arach·noi·dea 
 
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