The term 'smacking sound' can be represented by two crossword solutions: WHAP (4 letters) and SPLAT (5 letters). WHAP is an informal word used to describe a sharp, sudden sound, usually made when something is hit or slapped. SPLAT is a sound effect used to represent a wet, squishy sound, such as when a liquid or soft object is dropped or thrown. Both words are commonly used to describe the sound of something being smacked.