Definition of phyllidium in US English:

phyllidium

noun

Botany Zoology
  • Any of various small leaf-like structures in animals or plants; specifically (a) each of the lamellar folds of the mantle that act as gills in certain opisthobranch gastropods lacking ctenidia; (b) a plant part homologous to or resembling a leaf, especially a phyllid; (c) an appendage of the scolex in certain tapeworms (rare).

Origin

Late 19th century; earliest use found in The Century Dictionary. From ancient Greek ϕύλλον leaf + -idium. With sense (a) perhaps compare slightly earlier phyllidiobranchiate.

Pronunciation

phyllidium

/fɪˈlɪdɪəm/