The words deuce, douce sound the same but have different meanings and spellings. Why do deuce, douce sound the same even though they are completely different words?
The answer is simple: deuce, douce are homophones of the English language.
A playing card having two spots or the side of a die bearing two pips.
A cast of dice totaling two.
A tied score in tennis in which each player or side has 40 points, or 5 or more games, and one player or side must win 2 successive points to win the game, or 2 successive games to win the set.
To make the score of (a tennis game or set) deuce.
Sweet, nice, pleasant.
Serious and quiet; steady, not flighty or casual; sober.
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").