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Planck's constant the fundamental constant in quantum mechanics that expresses the ratio of the radiant energy of one quantum to the frequency of radiation.
plane1 a flat or level surface. [7 definitions]
plane2 any of various carpentry tools with an adjustable blade, used to make surfaces of wood smooth, true, grooved, or the like. [3 definitions]
plane geometry the geometry of two-dimensional or planar figures.
planer a person or thing that planes, esp. a machine that cuts or smooths wood.
planer tree a small elm tree with ovate leaves and bearing a small, nutlike fruit which grows in moist areas of the southeast United States.
planet a large, nonluminous celestial body, esp. one of the nine in the solar system, that revolves around a star and often has one or more satellites. [2 definitions]
planetable combined form of planet.
plane table a portable drawing board mounted on a tripod which is used by surveyors in the field.
planetarium an apparatus that projects a representation of the stars, planets, and the like, usu. upon a dome-shaped ceiling. [3 definitions]
planetary of, concerning, or like a planet or planets. [3 definitions]
planetesimal any of the numerous small bodies once thought to have orbited the sun and coalesced to form the planets.
planet-friendly of or pertaining to a product or process that causes minimal harm to the environment.
planet gear a gear that meshes with and describes a circular path around another gear, esp. in an epicyclic train; planet wheel.
planetoid an asteroid.
planet wheel see planet gear.
plangent sounding deeply or loudly. [2 definitions]
planimeter a device that measures the area of a plane figure by tracing around its entire perimeter.
planisphere a maplike projection of all or part of a sphere on a plane surface. [2 definitions]
plank a length of wood similar to, but thicker than, a board. [4 definitions]
planking planks collectively. [2 definitions]