The term 'SAD SOUND' can be represented by four different crossword solutions: KNELL (5 letters), MOAN (4 letters), SIGH (4 letters), and SOB (3 letters). A KNELL is a sound made by a bell, usually to signify a death or a funeral. A MOAN is a low, mournful sound, often expressing pain or sorrow. A SIGH is an expression of relief, disappointment, or sadness. Finally, a SOB is a sudden, convulsive sound made while crying. All of these sounds are associated with sadness and grief.