What is the pun( what are the two meanings) when John Hallock says "the affair was quite abovr board"?

pun is a poetic device used by writers to create double meanings of a single word 

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Pun means playing with words. Above board means to be honest. Here john uses it to console his wife that he was being honest and there was nothing sort of love relation with Helen contrary to what his nagging wife thought.

When John says the word 'above-board' he means that he was not involved with Helen. It was only that Helen was helping him with the ideas for ghost stories.He also clarified that there was nothing fishy in their relationship.He was very honest to her.There is pun on the word 'affair'.It only refers to the scandalous happening at party and the mis understood and miss interpreted affair.

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