What is Keff?
A light, polite fart.
He produced a fart, so quiet as to be almost a keff. Why, Dr Grierson! whispered Mrs Timmins, as she put her 'kerchief to her nose......
From 'Dr Grierson Makes a House Call' by Antonia Fraser.
See guff, trouser cough, grierson, air biscuit, pot pourri