The words epic, epoch sound the same but have different meanings and spellings. Why do epic, epoch sound the same even though they are completely different words?
The answer is simple: epic, epoch are homophones of the English language.
An extended narrative poem in elevated or dignified language, celebrating the feats of a legendary or traditional hero.
A literary or dramatic composition that resembles an extended narrative poem celebrating heroic feats.
A series of events considered appropriate to an epic: the epic of the Old West.
Of, constituting, having to do with, or suggestive of a literary epic: an epic poem.
A particular period of history, especially one considered remarkable or noteworthy.
A notable event that marks the beginning of such a period. See Synonyms at period.
A unit of geologic time that is a division of a period.
Astronomy An instant in time that is arbitrarily selected as a point of reference.
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").