The words cymbal, symbol sound the same but have different meanings and spellings. Why do cymbal, symbol sound the same even though they are completely different words?
The answer is simple: cymbal, symbol are homophones of the English language.
A percussion instrument consisting of a concave brass plate that makes a loud clashing tone when hit with a drumstick or when used in pairs.
Something that represents something else by association, resemblance, or convention, especially a material object used to represent something invisible. See Synonyms at sign.
A printed or written sign used to represent an operation, element, quantity, quality, or relation, as in mathematics or music.
Psychology An object or image that an individual unconsciously uses to represent repressed thoughts, feelings, or impulses: a phallic symbol.
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").