A chillum, or chilam, is a straight conical pipe with end-to-end channel, traditionally made of clay and used since at least the eighteenth century by as sadhus in India. It was invented in India. Traditionally, chillums are made of clay, stone or wood and have been used by the Sadhus (Holy Men) in India and by Hindu monks in the Himalayan area since at least the 18th century to smoke opium, cannabis and other narcotics or herbs.
Source: What is chillum? why sadhu smoke this?