The words saccharin, saccharine sound the same but have different meanings and spellings. Why do saccharin, saccharine sound the same even though they are completely different words?
The answer is simple: saccharin, saccharine are homophones of the English language.
A white crystalline powder, C7H5NO3S, having a taste about 500 times sweeter than cane sugar, used as a calorie-free sweetener.
Of, relating to, or characteristic of sugar or saccharin; sweet.
Having a cloyingly sweet attitude, tone, or character: a saccharine smile.
Excessively sentimental: "It was enough for him to rely on sentiment . . . and saccharine assertions about The Home” ( Kate Millett).
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.