What does aril or arillus mean?
The definition of aril and arillus
Ar”il, A*ril”lus, n.
Etym: [From LL. arilli dry grapes, perh. fr. L. aridus dry: cf. F,. arille.] (Bot.)

A exterior covering, forming a false coat or appendage to a seed, as the loose, transparent bag inclosing the seed or the white water lily. The mace of the nutmeg is also an aril. Gray.