The words ringer, wringer sound the same but have different meanings and spellings. Why do ringer, wringer sound the same even though they are completely different words?
The answer is simple: ringer, wringer are homophones of the English language.
Games A horseshoe or quoit thrown so that it encircles the peg.
One that rings, especially one that sounds a bell or chime.
Slang A contestant entered dishonestly into a competition.
Slang One who bears a striking resemblance to another: a ringer for his father.
One that wrings, especially a device in which laundry is pressed between rollers to extract water.
put (someone) through the wringer Slang To subject to a severe trial or ordeal.
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.