The words wen, when sound the same but have different meanings and spellings. Why do wen, when sound the same even though they are completely different words?
The answer is simple: wen, when are homophones of the English language.
A harmless cyst, especially on the scalp or face, containing the fatty secretion of a sebaceous gland.
Variant of wynn.
At what time: When will we leave?
At the time that: in the spring, when the snow melts.
As soon as: I'll call you when I get there.
Whenever: When the wind blows, all the doors rattle.
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").