In a word: Penumbra

August 08, 2011

Each week The Sun's John McIntyre presents a moderately obscure but evocative word with which you may not be familiar — another brick to add to the wall of your working vocabulary. This week's word:


Even shadows may not have sharply defined boundaries. The word penumbra (pronounced puh-NUM-bruh) refers generally to an area of partial shade. It comes from the Latin paene "almost" umbra "shadow."

More technically, a penumbra is the "partially shaded outer region of the shadow cast by an opaque object," the New Oxford American Dictionary says. In astronomy, there is an even more technical sense: the shadow that the earth or the moon casts in the course of a partial eclipse.

Though the word had been used in legal opinions by Justices Holmes and Cardozo and Judge Learned Hand, it received widespread notice from the opinion in Griswold v. Connecticut (1965) in which Justice William O. Douglas asserted that the Constitution includes an implied right to privacy:

"The foregoing cases suggest that specific guarantees in the Bill of Rights have a penumbra, formed by emanations from those guarantees that help give them life and substance."

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