Sentence:  The best <WSD>April fool</WSD> ever perpetrated was 1 April 1698 and made a laughing stock of the gentry of London, great numbers of whom turned up in their carriages and finery at the Tower of London to 'see the lions being washed' as instructed on their gilt-edged invitation cards. 
Meaning of the word marked with <WSD> tags:  A practical joke played on April Fools' Day.