The term 'sighing sound' can be represented by two crossword solutions: 'aah' (3 letters) and 'SOUGH' (5 letters). 'Aah' is an expression of surprise, admiration, or relief, while 'SOUGH' is a soft, rustling sound, such as the sound of wind in trees. Both words are used to describe a sighing sound, which is a sound made when someone exhales deeply in a way that expresses emotion, such as sadness, disappointment, or relief.