(topology) Informally, a set such that the target point of a movement by a small amount in any direction from any point in the set is still in the set; exemplified by a full circle without its boundary.

plural of dead-set

plural of dead set

(mathematical analysis) A set which is equal to its set of limit points. That is, a set A is perfect if A'=A.

(music) A wind instrument incorporating multiple pipes, such as a panpipe or bagpipe. / (idiomatic) Voice for singing.

plural of jet set

(logic) A set of natural numbers that can be defined by a formula of first-order Peano arithmetic.

plural of set piece

plural of box set

(underwater diving) The set of equipment required by a scuba diver to be at ease when submerged for extended periods of time. Modern equipment sets include tanks containing mixes of nitrogen in varied ratios with oxygen, a buoyancy control device, a first- and second-stage regulator (to allow the regulated flow of gas from the tank into the user's respiratory system), a wetsuit and accessories for heat insulation, fins for underwater propulsion, a mask (to see underwater), and a snorkel (for moving around the surface of the water without using up breathing gas). Many divers also choose to dive with a diving knife (in case of a tangle with a net, etc.), and night divers may also dive with a waterproof flashlight.