Definition of merostome in US English:

merostome

noun

Zoology
  • A chelicerate arthropod of the class Merostomata, of which the horseshoe crab is the only extant member.

Origin

Late 19th century; earliest use found in Smithsonian Institution Annual Reports. From mero- + -stome, after scientific Latin Merostomata, (former) suborder name.