Lesson : Shaddah : Sukun + Vowel on the same letter
In Arabic, when two of the same letter appears one after the other in the same word, it is considered a special situation. An example of this occurrence in the English language is the word 'FUNNY'. The 'N' comes twice consecutively in the same word. Although the letter is written twice in English, in Arabic, the letter is written once and a special symbol is placed atop the letter to indicate that the reader must pronounce it twice. There is more emphasis in the pronunciation of the doubled letter in Arabic than there is in English however.
The symbol which is placed atop the letter is called a shaddah or tashdeed. The letter which holds the shaddah is called mushaddad. The reality of the mushaddad letter is that it is a saakin letter followed by a mutaharrik letter of the same type. So, when we read mushaddad letters, we see one letter, but it is actually two; the first saakin, and the second mutaharrik. The haraka of the second may be any of the three and it is written either above or beneath the shaddah, not the letter itself.