The words cubit, qubit sound the same but have different meanings and spellings. Why do cubit, qubit sound the same even though they are completely different words?
The answer is simple: cubit, qubit 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.