Definition of cercus in US English:



  • A small appendage at the end of the abdomen of some insects and other arthropods, occurring in pairs.

    • ‘The cerci (tail appendages) begin to disarticulate.’
    • ‘They have no eyes, antennae, or caudal cerci but have a telson tail, which is common in crustaceans but absent in other hexapods.’
    • ‘In L. forcipatus females the ovipositor valves reach the tips of the cerci; in L. disjunctus they do not.’
    • ‘These species are notable for the plesiomorphic retention of venation (albeit already quite reduced) in their tegmina, segmented cerci, and pentamerous tarsi.’
    • ‘By analogy with modern arthropods this zone was inferred to lie at the anterior of a terminal ventral body segment-the telosoma and the antenniform cerci of Olenoides serratus might be interpreted as belonging to that segment.’


Early 19th century: from modern Latin, from Greek kerkos ‘tail’.