The words ceiling, sealing sound the same but have different meanings and spellings. Why do ceiling, sealing sound the same even though they are completely different words?
The answer is simple: ceiling, sealing are homophones of the English language.
The upper interior surface of a room.
Material used to cover this surface.
Something resembling a ceiling: a ceiling of leaves over the arbor.
An upper limit, especially as set by regulation: wage and price ceilings.
Used for closing securely.
Present participle of seal.
Action of the verb to seal in any sense.
Present participle of seal.
Definitions from The American Heritage® Dictionary of the English Language, 4th Edition, from Wiktionary, Creative Commons Attribution/Share-Alike License 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").