PLANE, n. [from L. planus. See Plain.] In geometry, an even or level surface, like plain in popular language.

1. In geometry, an even or level surface, like plain in popular language.
2. In astronomy, an imaginary surface supposed to pass through any of the curves described on the celestial sphere; as, the plane of the ecliptic; the plane of a planet's orbit; the plane of a great circle.
3. In mechanics. [See Plain figure.]
4. In joinery and cabinet work, an instrument consisting of a smooth piece of wood, with an aperture, through which passes obliquely a piece of edged steel or chisel, used in paring or smoothing boards or wood of any kind.

1. To make smooth; to pare off the inequalities of the surface of a board or other piece of wood by the use of a plane.
2. To free from inequalities of surface. – Arbuthnot.

1. Any tree of the genus Platanus.
   
   

   * The Oriental plane (Platanus orientalis) is a native of Asia. It rises with a straight, smooth, branching stem to a great height, with palmated leaves, and long pendulous peduncles, sustaining several heads of small close-sitting flowers. The seeds are downy, and collected into round, rough, hard balls. The Occidental plane (Platanus occidentalis), which grows to a great height, is a native of North America, where it is popularly called sycamore, buttonwood, and buttonball, names also applied to the California species (Platanus racemosa).

2. Without elevations or depressions; even; level; flat; lying in, or constituting, a plane; as, a plane surface.
   
   

   * In science, this word (instead of plain) is almost exclusively used to designate a flat or level surface.

   Plane angle, the angle included between two straight lines in a plane. -- Plane chart, Plane curve. See under Chart and Curve. -- Plane figure, a figure all points of which lie in the same plane. If bounded by straight lines it is a rectilinear plane figure, if by curved lines it is a curvilinear plane figure. -- Plane geometry, that part of geometry which treats of the relations and properties of plane figures. -- Plane problem, a problem which can be solved geometrically by the aid of the right line and circle only. -- Plane sailing (Naut.), the method of computing a ship's place and course on the supposition that the earth's surface is a plane. -- Plane scale (Naut.), a scale for the use of navigators, on which are graduated chords, sines, tangents, secants, rhumbs, geographical miles, etc. -- Plane surveying, surveying in which the curvature of the earth is disregarded; ordinary field and topographical surveying of tracts of moderate extent. -- Plane table, an instrument used for plotting the lines of a survey on paper in the field. -- Plane trigonometry, the branch of trigonometry in which its principles are applied to plane triangles.

3. A surface, real or imaginary, in which, if any two points are taken, the straight line which joins them lies wholly in that surface] or a surface, any section of which by a like surface is a straight line; a surface without curvature.
4. To make smooth] to level; to pare off the inequalities of the surface of, as of a board or other piece of wood, by the use of a plane; as, to plane a plank.
5. Of a boat, to lift more or less out of the water while in motion, after the manner of a hydroplane; to hydroplane.
6. An ideal surface, conceived as coinciding with, or containing, some designated astronomical line, circle, or other curve; as, the plane of an orbit; the plane of the ecliptic, or of the equator.
7. To efface or remove.
   
   

   He planed away the names . . . written on his tables. Chaucer.

8. A block or plate having a perfectly flat surface, used as a standard of flatness; a surface plate.
9. Figuratively, to make plain or smooth.
   
   
   [R.]

   What student came but that you planed her path. Tennyson.

10. A tool for smoothing boards or other surfaces of wood, for forming moldings, etc. It consists of a smooth-soled stock, usually of wood, from the under side or face of which projects slightly the steel cutting edge of a chisel, called the iron, which inclines backward, with an apperture in front for the escape of shavings; as, the jack plane; the smoothing plane; the molding plane, etc.
    
    

    Objective plane (Surv.), the horizontal plane upon which the object which is to be delineated, or whose place is to be determined, is supposed to stand. -- Perspective plane. See Perspective. -- Plane at infinity (Geom.), a plane in which points infinitely distant are conceived as situated. -- Plane iron, the cutting chisel of a joiner's plane. -- Plane of polarization. (Opt.) See Polarization. -- Plane of projection. (a) The plane on which the projection is made, corresponding to the perspective plane in perspective; -- called also principal plane. (b) (Descriptive Geom.) One of the planes to which points are referred for the purpose of determining their relative position in space. -- Plane of refraction or reflection (Opt.), the plane in which lie both the incident ray and the refracted or reflected ray.