The term 'cluck of disapproval' is an expression used to describe the sound made by a person or animal when they are expressing disapproval or dissatisfaction. The crossword solutions for this term are TSK (3 letters) and TCH (3 letters). TSK is an onomatopoeic sound used to express disapproval, while TCH is a sound made to express sympathy or understanding. Both of these sounds are commonly used to express disapproval or dissatisfaction in a non-verbal way.