The correct spelling of "un did" is actually "undid", pronounced as /ʌnˈdɪd/. This word is derived from the prefix "un-" meaning "not" or "reverse" and the verb "do". The letter "n" represents the sound of the prefix and the "di" are represented by the letters "d" and "i" respectively. Therefore, it is important to remember to use all the letters in the correct order when spelling "undid" to avoid confusion or miscommunication.