boundary

/ˈbaʊndəri/

/ˈbaʊndri/

Other forms: boundaries

If you play a sport you are familiar with the term "in bounds," which refers to the boundary, or limits of the playing field that the players must stay within. It is also the outer limits of any space.

A boundary is a border and it can be physical, such as a fence between two properties, or abstract, such as a moral boundary that society decides it is wrong to cross. If you have no sense of boundaries, you probably annoy people sometimes by getting too close to them or talking about inappropriate topics. Gustave Flaubert once said, “Earth has its boundaries, but human stupidity is limitless.” A boundary is basically what limits us.

Definitions of boundary

1. noun

   the line or plane indicating the limit or extent of something
   synonyms: bound, bounds

   examples:

   Rubicon

   the boundary in ancient times between Italy and Gaul; Caesar's crossing it with his army in 49 BC was an act of war

   Mohorovicic discontinuity

   the boundary between the Earth's crust and the underlying mantle

   types:

   hairline

   the natural margin formed by hair on the head

   frontier

   an international boundary or the area (often fortified) immediately inside the boundary

   heliopause

   the boundary marking the edge of the sun's influence; the boundary (roughly 100 AU from the sun) between the interplanetary medium and the interstellar medium; where the solar wind from the sun and the radiation from other stars meet

   border, borderline, boundary line, delimitation, mete

   a line that indicates a boundary

   bourn, bourne

   an archaic term for a boundary

   district line

   the boundary between two districts

   county line

   the boundary between two counties

   city line

   the boundary of a city

   border, edge

   the boundary of a surface

   end

   a boundary marking the extremities of something

   demarcation, demarcation line, limit

   the boundary of a specific area

   lineation, outline

   the line that appears to bound an object

   surface

   the extended two-dimensional outer boundary of a three-dimensional object

   shoreline

   a boundary line between land and water

   edge

   the outside limit of an object or area or surface; a place farthest away from the center of something

   interface

   (chemistry) a surface forming a common boundary between two things (two objects or liquids or chemical phases)

   hard palate

   the bony part of the roof of the mouth

   palate, roof of the mouth

   the upper surface of the mouth that separates the oral and nasal cavities

   face, side

   a surface forming part of the outside of an object

   circuit, circumference

   the boundary line encompassing an area or object

   fence line

   a boundary line created by a fence

   property line

   the boundary line between two pieces of property

   state boundary, state line

   the boundary between two states

   brink

   the edge of a steep place

   celestial sphere, empyrean, firmament, heavens, sphere, vault of heaven, welkin

   the apparent surface of the imaginary sphere on which celestial bodies appear to be projected

   city limit, city limits

   the limits of the area occupied by a city or town

   end

   the surface at either extremity of a three-dimensional object

   inside, interior

   the inner or enclosed surface of something

   limb

   (astronomy) the circumferential edge of the apparent disc of the sun or the moon or a planet

   upper limit

   the limit on the upper (or northernmost) side of something

   lower limit

   the limit on the lower (or southernmost) side of something

   coastline

   the outline of a coast

   silhouette

   an outline of a solid object (as cast by its shadow)

   exterior, outside

   the outer side or surface of something

   skyline

   the outline of objects seen against the sky

   substrate, substratum

   a surface on which an organism grows or is attached

   three-mile limit

   the limit of a nation's territorial waters

   wave front, wavefront

   (physics) an imaginary surface joining all points in space that are reached at the same instant by a wave propagating through a medium

   photosphere

   the intensely luminous surface of a star (especially the sun)

   type of:

   extremity

   the outermost or farthest region or point
2. noun

   a line determining the limits of an area
   synonyms: bound, edge

   types:

   rim

   the shape of a raised edge of a more or less circular object

   border, margin, perimeter

   the boundary line or the area immediately inside the boundary

   fringe, outer boundary, periphery

   the outside boundary or surface of something

   brink, threshold, verge

   a region marking a boundary

   upper bound

   (mathematics) a number equal to or greater than any other number in a given set

   lower bound

   (mathematics) a number equal to or less than any other number in a given set

   thalweg

   the middle of the chief navigable channel of a waterway that forms the boundary line between states

   lip

   either the outer margin or the inner margin of the aperture of a gastropod's shell

   type of:

   line

   a length (straight or curved) without breadth or thickness; the trace of a moving point
3. noun

   the greatest possible degree of something
   synonyms: bound, limit

   types:

   knife-edge

   a narrow boundary

   absoluteness, starkness, utterness

   the quality of being complete or utter or extreme

   heat barrier, thermal barrier

   a limit to high speed flight imposed by aerodynamic heating

   level best, maximum, utmost, uttermost

   the greatest possible degree

   brink, cusp, verge

   the limit beyond which something happens or changes

   precipice

   the brink of a dangerous or potentially disastrous situation

   type of:

   extent

   the distance or area or volume over which something extends