1. The first (anterior) major body section or head plus the abdomen (opisthosoma), which may also include lateral appendages as well as the tail, if it exists.
2. The region near the head of spiders and some related arthropods, composed of fused segments of head and thorax.
3. The anterior or cephalic (head) portion of the body of certain invertebrates; such as, arachnids (spiders), in which segmentation is not evident.