The words qubit, cubit sound the same but have different meanings and spellings. Why do qubit, cubit sound the same even though they are completely different words?
The answer is simple: qubit, cubit are homophones of the English language.
An ancient unit of linear measure, originally equal to the length of the forearm from the tip of the middle finger to the elbow, or about 17 to 22 inches (43 to 56 centimeters).
A quantum bit.
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").