Rat-tat is an onomatopoeic word that is used to describe the sharp, rapid sound produced by a series of quick knocks or taps. There are a variety of synonyms that can be used to describe this sound including tat-tat, tap-tap, knock-knock, rap-rap, and drum-drum, among others. These words can be used interchangeably depending on the context in which they are used. For example, tat-tat and knock-knock may be used to describe the sound of a woodpecker, while rap-rap and drum-drum may be used to describe the sound of a drummer. Regardless of the word used to describe it, the rat-tat sound is distinctive and can be used to add emphasis or create a sense of urgency in writing.