The words bloc, block sound the same but have different meanings and spellings. Why do bloc, block sound the same even though they are completely different words?
The answer is simple: bloc, block are homophones of the English language.
A group of nations, parties, or persons united for common action: the Communist bloc.
An often bipartisan coalition of legislators acting together for a common purpose or interest: the farm bloc in the U.S. Senate.
A solid piece of a hard substance, such as wood, having one or more flat sides.
Such a piece used as a construction member or as a support.
Such a piece upon which chopping or cutting is done: a butcher's block.
Such a piece upon which persons are beheaded.
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.