The term 'invisible quality' can be summarized by the crossword solution 'AURA, ' which is a four-letter word. An AURA is an invisible quality or atmosphere that surrounds a person or object, and is often associated with a sense of mystery or power. It is believed to be composed of energy fields that are emitted from the body, and can be sensed by others. Auras are often used in spiritual practices, such as meditation and healing.