This is just another way of spelling 'siphon' — same word, same sound (SY-fun), same meanings. It is the British spelling, and even in Britain 'siphon' is now the more common of the two, so treat 'syphon' as a variant you should recognise when you read rather than one you need to write. The meanings are these. As a noun, a syphon is a bent tube used to move liquid out of a container: you fill the tube, put one end in the liquid and the other end lower down outside, and the liquid keeps flowing on its own — no pump needed. A 'soda syphon' is also a bottle that shoots fizzy water out when you press a handle; you see them in old films and in cocktail bars. As a verb, to syphon something is to move liquid that way, most often out of a tank — people syphon petrol out of a car. And there is a very common figurative use: to syphon off money means to take money out of a business or a fund quietly and dishonestly, a little at a time. That last meaning appears in the news constantly, and it is the one most students will actually meet.