an intricate knot tied by Gordius, the king of Phrygia, and cut by the sword of Alexander the Great after he heard that whoever undid it would become ruler of Asia
any very difficult problem; insoluble in its own terms
a common stock of a nationally known company whose value and dividends are reliable; typically have high price and low yield; "blue chips are usually safe investments"
the flash of light that accompanies an electric discharge in the atmosphere (or something resembling such a flash); can scintillate for a second or more
abrupt electric discharge from cloud to cloud or from cloud to earth accompanied by the emission of light