The words leaver, lever sound the same but have different meanings and spellings. Why do leaver, lever sound the same even though they are completely different words?
The answer is simple: leaver, lever are homophones of the English language.
One who leaves.
A simple machine consisting of a rigid bar pivoted on a fixed point and used to transmit force, as in raising or moving a weight at one end by pushing down on the other.
A projecting handle used to adjust or operate a mechanism.
A means of accomplishing; a tool: used friendship as a lever to obtain advancement.
To move or lift with or as if with a lever.
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").