The words vial, vile, viol sound the same but have different meanings and spellings. Why do vial, vile, viol sound the same even though they are completely different words?
The answer is simple: vial, vile, viol are homophones of the English language.
A small container, usually with a closure, used especially for liquids.
To put or keep in or as if in a vial.
Loathsome; disgusting: vile language.
Unpleasant or objectionable: vile weather. See Synonyms at offensive.
Contemptibly low in worth or account; second-rate.
Of mean or low condition.
Any of a family of stringed instruments, chiefly of the 16th and 17th centuries, having a fretted fingerboard, usually six strings, and a flat back and played with a curved bow.
See viola da gamba.
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.