Definition of Ontario
1 province of eastern Canada between the Great Lakes and Hudson Bay and bordering on the United States (New York, Michigan, and Minnesota); capital Toronto area 350,814 square miles (908,608 square kilometers), population 12,851,821 ◆Ontario is the most populous province of Canada.
2 city in southwestern California northwest of Riverside population 163,924
Ontarianplay \-ē-ən\ adjective or noun
ONTARIO Defined for English Language Learners
Definition of Ontario for English Language Learners
: province of Canada
: U.S. city, California
Lake Ontario : lake in the U.S. and Canada
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Britannica.com: Encyclopedia article about Ontario
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