Cupule

Definition
noun, plural: cupulas
(1) (botany) A plant structure made of hardened, cohering bracts, resembling a cup, as in acorn.
(2) (botany) A cup-like outgrowth of the thallus in some liverworts.
(3) (mycology) The apothecium of a cup fungus.
(4) (zoology) A small cup-shaped structure or body part, such as the suckers on the feet of some flies.
Supplement
(botany) The cupule, together with the calybium, makes up the accessory fruit of some flowering plants (e.g. Fagaceae). In some genera, the cupule may even develop sharp spines, such as in Castanea. This type of cupule renders protection from seed predators.
Word origin: Late Latin cūpula, little cask, diminutive of Latin cūpa, tub.