The words tel, tell sound the same but have different meanings and spellings. Why do tel, tell sound the same even though they are completely different words?
The answer is simple: tel, tell are homophones of the English language.
A hill or mound. Used especially for land features in the Middle East and North Africa
To give a detailed account of; narrate: tell what happened; told us a story.
To communicate by speech or writing; express with words: tell the truth; tell one's love.
To make known; reveal: tell a secret; tell fortunes.
To notify; inform.
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").