The term 'hammer sound' refers to the sound made when a hammer is used. The three crossword solutions for this term are BAM (3 letters), BANG (4 letters), and RAP (3 letters). BAM is a short, sharp sound made when a hammer strikes an object. BANG is a louder, more forceful sound made when a hammer strikes an object. RAP is a quick succession of hammer strikes. All three words describe the sound made when a hammer is used.