The correct spelling of the word is actually "sunder," which is pronounced /ˈsʌndər/. The word means to break apart, divide, or separate. It is derived from the Old English word sundrian, which has the same meaning. The spelling of the word "synder" is incorrect and may be a common misspelling or a result of a typographical error. Proper use of spelling and phonetics is essential to effective communication in both written and oral communication.