The term 'vanishing act word' is a crossword solution for the word 'POOF', which is a four-letter word. It is an expression used to describe something that has suddenly disappeared or vanished without a trace. This phrase is often used in the context of magic tricks, where a magician makes an object or person disappear in a puff of smoke. It can also be used to describe a situation where someone or something has suddenly and unexpectedly disappeared.