“Problems of fringe meaning are sometimes spoken of as ‘problems of the penumbra’, the point being that, in the case of a great many words, there is no doubt about the hard core of their meanings, but different views may well be taken on the question whether the words are applicable to things or situations outside that hard core.” Rupert Cross, Statutory Interpretation 57 (1976).
penumbra
penumbra (pi-n[schwa]m-br[schwa]), n. A surrounding area or periphery of uncertain extent. • In constitutional law, the Supreme Court has ruled that the specific guarantees in the Bill of Rights have penumbras containing implied rights, esp. the right of privacy. Pl. penumbras, penumbrae (pi-n[ schwa]m-bree). — penumbral (pi-n[schwa]m-br[schwa]l), adj.