Dal is the eighth letter of the modern Arabic order and the fourth of the older abjad order, from which it takes the numeral value four. It is one of the smallest letters in the script, a short angular hook that sits on the line and takes up little more room than a dot. It carries no pointing of its own, and the same hook marked with a single dot above is dhal, one of the six letters Arabic added to the alphabet it inherited.
Dal belongs to the group of six letters that join only to the right. A connected group of Arabic writing therefore ends whenever a dal is reached, and the next letter starts a fresh group. Six letters out of twenty-eight behave this way, and because several of them are among the commonest in the language, the effect on the look of a written line is considerable: Arabic words are not single unbroken chains but sequences of connected clusters separated by narrow gaps. Learners often read those gaps as word breaks, which they are not.
Dal is a sun letter, so the lam of the definite article assimilates to it in speech and is not heard, although it is still written. Its name descends from the Northwest Semitic daleth, whose sense was door, and the letter is the direct cognate of Hebrew dalet, Syriac dalath and the corresponding Samaritan letter. The Arabic name preserves the form of the older word and none of its meaning.