The words repost, riposte sound the same but have different meanings and spellings. Why do repost, riposte sound the same even though they are completely different words?
The answer is simple: repost, riposte are homophones of the English language.
To post again
To riposte: to strike back after parrying an attack
Sports A quick thrust given after parrying an opponent's lunge in fencing.
A retaliatory action, maneuver, or retort.
To make a return thrust.
To retort quickly.
Definitions from Wiktionary, Creative Commons Attribution/Share-Alike License, 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").