The term 'Sound of Disappointment' can be represented by two crossword solutions: TSK (3 letters) and GROAN (5 letters). TSK is an interjection used to express disapproval, disappointment, or disbelief. It is often used in response to someone's bad behavior or a mistake. GROAN is a low, mournful sound made in response to pain, disappointment, or frustration. It is usually uttered involuntarily and can be heard when someone is feeling overwhelmed or frustrated.