(topology) A set whose complement is open.

(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.

(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.

To depart on a voyage by boat.

Alternative spelling of heavyset

Alternative spelling of set-theoretic

(linguistics) A set of concepts whose names are coordinate terms.

Alternative spelling of downset

(computing) The set of machine instructions that a particular CPU can execute; the corresponding set of assembly language mnemonics.

To attack someone. / To begin an activity; to embark upon a course of action.