The words oar, or, ore sound the same but have different meanings and spellings. Why do oar, or, ore sound the same even though they are completely different words?
The answer is simple: oar, or, ore are homophones of the English language.
A long, thin, usually wooden pole with a blade at one end, used to row or steer a boat.
A person who rows a boat, especially in a race.
To propel with or as if with oars or an oar.
To traverse with or as if with oars or an oar: an hour to oar the strait.
Used to indicate an alternative, usually only before the last term of a series: hot or cold; this, that, or the other.
Used to indicate the second of two alternatives, the first being preceded by either or whether: Your answer is either ingenious or wrong. I didn't know whether to laugh or cry.
Archaic Used to indicate the first of two alternatives, with the force of either or whether.
Used to indicate a synonymous or equivalent expression: acrophobia, or fear of great heights.
A mineral or an aggregate of minerals from which a valuable constituent, especially a metal, can be profitably mined or extracted.
Definitions from The American Heritage® Dictionary of the English Language, 4th Edition and Wordnik.
Homophones (literally "same sound") are usually defined as words that share the same pronunciation, regardless of how they are spelled.
If they are spelled the same then they are also homographs (and homonyms); if they are spelled differently then they are also heterographs (literally "different writing").