The words breach, breech sound the same but have different meanings and spellings. Why do breach, breech sound the same even though they are completely different words?
The answer is simple: breach, breech are homophones of the English language.
An opening, a tear, or a rupture.
A gap or rift, especially in or as if in a solid structure such as a dike or fortification.
A violation or infraction, as of a law, a legal obligation, or a promise.
A breaking up or disruption of friendly relations; an estrangement.
The lower rear portion of the human trunk; the buttocks.
A breech presentation or delivery.
A fetus in breech presentation.
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").