The hijā’ī order groups letters by similarity of shape and is used in places where lists of names and words need to be sorted, such as phonebooks, classroom lists, and dictionaries. However, the newer hijāʾī order is what modern dictionaries use for alphabetical sorting; this is because it allows forletters to be partially grouped together based on similarities in shape. Additionally, the hijāʾī order can never be used as numerals.

The madda ⟨مَدّة⟩is a tilde-shaped diacritic which, in Arabic, can only appear on top of an alif and indicates a glottal stop followed by a long /aː/. The same sequence /ʔaː/ could also be represented by two alifs. However, consecutive alifs are never used in Arabic orthography. Instead, this sequence must always be written as a single alif with the maddah above it – this combination is known as an alif maddah.

Example: قُرْآن /qurˈʔaːn/ 🠊 Qur’an

The sukūn ⟨سُكُونْ⟩ is a diacritic in the shape of a circle, placed above a letter ( ْ). It signifies that the consonant it is attached to does not have a vowel following it, i.e., there is no vowel sound. This symbol is essential for writing consonant-vowel-consonant syllables, which are quite common in Arabic.

Example: دَدْ /dad/

The shadda ⟨شَدّة⟩ is a diacritic symbol that geminate, or double consonants which are phonemic in Arabic. It written above the letters to be doubled, and it is -the only ḥarakah- used commonly in spelling to avert ambiguity.

Example: دّ /dd/; madrasa ⟨مَدْرَسَة⟩ (school) vs. mudarrisah ⟨مُدَرِّسَة⟩ (teacher, female)

The tanwīn ⟨تَنْوِين⟩ represents the consonant /n/ that follows the three vowel diacritics (fatḥa, ḍamma and kasra) when doubled at the end of a word. The signs from right to left respectively denote -un, -in, and -an. These endings are generally used whenever a word is indefinite in Arabic.

The tanwīn fatha is typically written in unvocalized texts because the letter alif should always be written along with (except for words ending in tā’ marbūṭa, hamza or diptotes).

Here are the grammatical cases and tanwīn endings in indefinite triptote forms:
-un: nominative case.
-an: accusative case (also functions as an adverbial marker).
-in: genitive case.

The waṣla ⟨وَصْلة⟩ (meaning ’an instance of connection’) or hamzatu l-waṣli ⟨هَمْزةُ الوَصْل⟩ is an Arabic diacritic sometimes placed over the letter ʾalif at the beginning of the word. It indicates that the alif is not pronounced as a glottal stop (written with the letter or diacritic hamza ء), but that the word is connected to the previous word (like liaison in French). Outside of vocalised liturgical texts, the waṣla is usually not written.

The other fourteen letters are called moon letters, because the first letter, ق /q/, of the Arabic word for ‘moon’, قَمَرٌ (qamarun), represents the class of non-assimilating letters. In other words as opposed to ‘sun letters’ they do not cause the sound لـ /l/, of the definite article, to blend in with it.

For example: ‘the moon’ written al-qamar would be pronounced the same way (al-qamar and not aq-qamar). Same goes with any other ‘moon letter’.​​