The words gros, grow sound the same but have different meanings and spellings. Why do gros, grow sound the same even though they are completely different words?
The answer is simple: gros, grow are homophones of the English language.
A heavy silk with a dull finish
To increase in size by a natural process.
To expand; gain: The business grew under new owners.
To increase in amount or degree; intensify: The suspense grew.
To develop and reach maturity.
Definitions from the GNU version of the Collaborative International Dictionary of English, 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").