dyke [OE] There are two almost contradictory aspects to dyke: it means both ‘something dug out’ and ‘something built up’. The first group of senses corresponds to the variant ditch [OE] and is related to dig [ME]. At much the same time related German and Dutch forms gave us the second group, initially in the sense ‘a city wall, a fortification’. A possible linking idea appears in the sense ‘dam’—a dam entails both the building up of an obstruction and the creation of a pool. The Dutch build dykes to prevent flooding from the sea. This is the context of the phrase to put your finger in a dyke, ‘to attempt to stem the advance of something undesirable’. It comes from a story of a heroic little Dutch boy who saved his community from flooding, by placing his finger in a hole in a dyke, thereby preventing it getting bigger and averting the disastrous consequences, popularized by the 1865 novel Hans Brinker, or the Silver Skates by American author Mary Mapes Dodge.

The word dyke is also a derogatory term for a lesbian, especially a masculine-looking one. Originally found in the fuller form bulldyke, it has been in use since at least the 1930s, but no one is sure of its origin.