The words tenuis, tenuous sound the same but have different meanings and spellings. Why do tenuis, tenuous sound the same even though they are completely different words?
The answer is simple: tenuis, tenuous are homophones of the English language.
Linguistics A voiceless unaspirated stop in ancient Greek.
Linguistics A voiceless stop.
Having little substance; flimsy: a tenuous argument.
Having a thin consistency; dilute.
Long and thin; slender: tenuous strands.
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.