from Wiktionary, Creative Commons Attribution/Share-Alike License
- proper n. A taxonomic order within the class Merostomata — distinguished from all other chelicerates by having compound eyes. The only living xiphosurans are the horseshoe crabs.
From Ancient Greek ξίφος (xiphos, "sword") and οὐρά (oura, "tail"), in reference to the long, slender, stiff tail of the horseshoe crab. (Wiktionary)