Boundary \Bound"a*ry\, n.; pl. Boundaries [From Bound a limit; cf. LL. bonnarium piece of land with fixed limits.]

That which indicates or fixes a limit or extent, or marks a bound, as of a territory; a bounding or separating line; a real or imaginary limit.

But still his native country lies Beyond the boundaries of the skies. --N. Cotton.

That bright and tranquil stream, the boundary of Louth and Meath. --Macaulay.

Sensation and reflection are the boundaries of our thoughts. --Locke.

Syn: Limit; bound; border; term; termination; barrier; verge; confines; precinct.

Usage: Bound, Boundary. Boundary, in its original and strictest sense, is a visible object or mark indicating a limit. Bound is the limit itself. But in ordinary usage the two words are made interchangeable.

Source: Webster's Revised Unabridged Dictionary (1913)