The words bole, boll, bowl sound the same but have different meanings and spellings. Why do bole, boll, bowl sound the same even though they are completely different words?
The answer is simple: bole, boll, bowl are homophones of the English language.
The trunk of a tree.
Any of various soft fine clays, especially a reddish-brown variety used as a pigment.
A moderate reddish brown.
The seed-bearing capsule of certain plants, especially cotton and flax.
A hemispherical vessel, wider than it is deep, used for holding food or fluids.
The contents of such a vessel.
A drinking goblet.
A bowl-shaped part, as of a spoon or pipe.
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").