Today’s name that just popped into my head, for no reason I could think of. From NOAD2:
penumbra the partially shaded outer region of the shadow cast by an opaque object. [also figurative uses] ORIGIN mid 17th cent.: modern Latin, from Latin paene ‘almost’ + umbra ‘shadow’ [OED3 (Sept. 2005): Johannes Kepler Ad Vitellionem Paralipomena (1604)]
I think it’s wonderful that this was devised by Kepler as a technical term in astronomy. As a technical term in English it comes paired with umbra:
the fully shaded inner region of a shadow cast by an opaque object, especially the area on the earth or moon experiencing the total phase of an eclipse. (NOAD2)
A diagram illustrating both terms, without the complexities of eclipses:
Two parts to the word penumbra, pen(e)- and umbra, each putting the word into relationships with a cluster of other words in English.