Whap is a slang term used to describe the sound of a quick, sharp blow. There are several words that can be used as a synonym for whap, including slap, smack, thwack, and whack. All of these words refer to a similar action or sound, but they each have their own unique connotations. For example, slap is often associated with an open-handed strike, while whack typically refers to a harder or more forceful blow. Thwack has a slightly more onomatopoeic quality and suggests a more solid, dull sound. Regardless of which word is used, they all convey a sense of speed and impact that can be used to add emphasis or intensity to a story or description.