The words synching, sinking sound the same but have different meanings and spellings. Why do synching, sinking sound the same even though they are completely different words?
The answer is simple: synching, sinking are homophones of the English language.
Present participle of sink.
The act or process of sinking.
Present participle of synch.
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.