In English, when a consonant is doubled in the same word, meaning the first syllable ends in the same letter that the second syllable starts with (e.g. funny 'fun-ny'), both consonants are written separately. When this happens in Arabic, the letter is only written once, and the symbol () is placed upon it to indicate duplication in pronunciation.
In the Arabic language, meanings are established by placing base letters side by side in designated patterns. Mostly all combinations of three consonants have been assigned distinct meanings and whenever those consonants appear in a given word, depending on the pattern of vowellization, the base letter meaning will be conveyed in a unique way.