From bound +‎ -ary, Old French, from Latin.

• (UK) IPA^(key): /ˈbaʊndɹi/
• (US) IPA^(key): /ˈbaʊndəɹi/

• Audio (US):

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• Audio (General Australian):

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• Rhymes: -aʊndɹi

boundary (plural boundaries)

1. The dividing line or location between two areas.
   • 1908, W[illiam] B[lair] M[orton] Ferguson, chapter IV, in Zollenstein, New York, N.Y.: D. Appleton & Company, →OCLC, page 40:

     So this was my future home, I thought![…]Backed by towering hills, the but faintly discernible purple line of the French boundary off to the southwest, a sky of palest Gobelin flecked with fat, fleecy little clouds, it in truth looked a dear little city; the city of one's dreams.

   • 2017 October, Juin-Jen Chang, Ching-Chong Lai, Ping Wang, “A Tale of Two Cities: Cross-Border Casino Competition Between Detroit and Windsor”, in NBER WORKING PAPER SERIES‎^[1], archived from the original on 15 August 2021, page 1:

     City or national boundaries are locations of economic opportunity, especially if the existence of the border is itself the source of a monopoly situation that favors one side over the other (Krakover, 1997).

2. (figurative, often in the plural) The bounds, confines, or limits between immaterial things (such as one’s comfort zone, privacy, or professional sphere and the realm beyond).

   I didn’t mean to push the boundaries by sending my boss a message on Saturday night.

3. (cricket) An edge or line marking an edge of the playing field.
4. (cricket) An event whereby the ball is struck and either touches or passes over a boundary (with or without bouncing), usually resulting in an award of 4 (four) or 6 (six) runs respectively for the batting team.

   Travis hit a boundary to seal the match on the last ball of the over.

5. (topology) (of a set) The set of points in the closure of a set 👁 {\displaystyle S}
   , not belonging to the interior of that set.
6. (Philippines) Commission paid by a bus or jeepney driver to a public transportation operator for taking passengers, or the excess collected fares taken as daily wage.

• “boundary”, in Webster’s Revised Unabridged Dictionary, Springfield, Mass.: G. & C. Merriam, 1913, →OCLC.
• William Dwight Whitney, Benjamin E[li] Smith, editors (1911), “boundary”, in The Century Dictionary[…], New York, N.Y.: The Century Co., →OCLC.