The term 'Sound of Reproof' refers to a type of sound that is used to express disapproval or criticism. The three crossword solutions for this term are TUT (3 letters), HOOT (4 letters), and TSK (3 letters). TUT is an expression of disapproval, usually uttered in a low voice. HOOT is a loud, sharp sound made to express disapproval or derision. TSK is a sound made with the tongue to express disapproval or disappointment. All three of these sounds are used to express disapproval or criticism, and can be considered a 'sound of reproof'.