Merriam-Webster Collegiate Dictionary - penumbra

 noun  (plural ~e or -bras)  Etymology: New Latin, from Latin paene almost + umbra shadow — more at umbrage  Date: 1666  1.  a. a space of partial illumination (as in an eclipse) between the perfect shadow on all sides and the full light  b. a shaded region surrounding the dark central portion of a sunspot  2. a surrounding or adjoining region in which something exists in a lesser degree ; fringe  3. a body of rights held to be guaranteed by implication in a civil constitution  4. something that covers, surrounds, or obscures ; shroud a ~ of secrecy a ~ of somber dignity has descended over his reputation — James Atlas  • ~l adjective