The words strider, stridor sound the same but have different meanings and spellings. Why do strider, stridor sound the same even though they are completely different words?
The answer is simple: strider, stridor are homophones of the English language.
One who strides.
An insect called the water strider.
A harsh, shrill, grating, or creaking sound.
Pathology A harsh, high-pitched sound in inhalation or exhalation.
Definitions from Wiktionary, Creative Commons Attribution/Share-Alike License, 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.