A siphon is a tube or pipe that moves liquid from one container to another using gravity and air pressure, without any pumping. You've probably seen someone start a siphon by getting water flowing through a hose connected to a fish tank: once the liquid starts moving, it keeps flowing on its own until the higher container empties or the tube is lifted above the water level.

The science behind siphons is fascinating: gravity pulls the liquid down the longer end of the tube, and that pulling motion creates a vacuum that draws more liquid up and over from the higher container. Ancient Roman engineers used siphons in their aqueducts to move water across valleys.

The word also means to gradually take something away, often secretly or unfairly. A dishonest treasurer might siphon money from the club's account bit by bit, hoping no one notices. You could say that video games siphon away your study time when you play too much, or that a long, boring speech siphons the energy from a room. In this sense, siphon suggests something being drained away steadily, just like water flowing through that tube.