[ on-tair-ee-oh ]

  1. a province in southern Canada, bordering on the Great Lakes. 412,582 square miles (1,068,585 square kilometers). Capital: Toronto.

  2. Lake Ontario, a lake between the northeastern United States and southern Canada, between New York and Ontario province: the smallest of the Great Lakes. 193 miles (310 kilometers) long; 7,540 square miles (19,530 square kilometers).

  1. a city in southwestern California, east of Los Angeles.

Other words from Ontario

  • On·tar·i·an, On·tar·ic [on-tar-ik], /ɒnˈtær ɪk/, adjective, noun

Words Nearby Ontario

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

How to use Ontario in a sentence

  • Dane turned and laughed at him as he signed to one of the Ontario hired men to take the near horse's head.

    Winston of the Prairie | Harold Bindloss
  • Thus in the Laurentian Lakes above Ontario the geologist finds evidence that the drainage lines have again and again been changed.

    Outlines of the Earth's History | Nathaniel Southgate Shaler
  • At a later stage channels were formed leading from Georgian Bay to the eastern part of Ontario.

    Outlines of the Earth's History | Nathaniel Southgate Shaler
  • What Ontario lacks in salt water navigation is, however, made up by the busy traffic of the Great Lakes.

  • I had, yesterday, quite an interesting excursion to one of these ancient places of sepulture north of the head of Lake Ontario.

    The Indian in his Wigwam | Henry R. Schoolcraft

British Dictionary definitions for Ontario


/ (ɒnˈtɛərɪəʊ) /

  1. a province of central Canada: lies mostly on the Canadian Shield and contains the fertile plain of the lower Great Lakes and the St Lawrence River, one of the world's leading industrial areas; the second largest and the most populous province. Capital: Toronto. Pop: 12 392 721 (2004 est). Area: 891 198 sq km (344 092 sq miles): Abbreviation: Ont., ON

  2. Lake Ontario a lake between the US and Canada, bordering on New York State and Ontario province: the smallest of the Great Lakes; linked with Lake Erie by the Niagara River and Welland Canal; drained by the St Lawrence. Area: 19 684 sq km (7600 sq miles)

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Cultural definitions for Ontario


Province in central Canada, bordered by Hudson Bay and James Bay to the north; Quebec to the east; the St. Lawrence River, Lake Ontario, Lake Erie, Lake Huron, Lake Superior, and Minnesota to the south; and Manitoba to the west. Its capital and largest city is Toronto.

Notes for Ontario

The Canadian side of Niagara Falls is in southern Ontario.

Notes for Ontario

Ottawa, Canada's capital, is in southeastern Ontario.

Notes for Ontario

Ontario is the most heavily industrialized, populous, and prosperous province in Canada.

The New Dictionary of Cultural Literacy, Third Edition Copyright © 2005 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.