The words gradients, gradience sound the same but have different meanings and spellings. Why do gradients, gradience sound the same even though they are completely different words?
The answer is simple: gradients, gradience are homophones of the English language.
The absence of a clear boundary, or the presence of a continuous spectrum of meaning, between two words or categories
Plural form of gradient.
Definitions 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.