The term 'Mysterious Quality' can be described by the crossword solution 'AURA', which is a four-letter word. An AURA is an invisible field of energy that surrounds living things, and is often associated with a sense of mystery. It is believed to be composed of spiritual, emotional, and physical energies, and can be sensed by some people. Auras are often seen as a sign of spiritual power or enlightenment, and can be used to help identify a person's character or personality.