Zay is the eleventh letter of the modern Arabic order and the seventh of the older abjad order, from which it takes the numeral value seven. It is written as the ra stroke carrying a single dot above it, and like ra it joins only to the right, so it closes its connected group. Its sound is the voiced alveolar sibilant, the z of English, the voiced counterpart of sin.
Zay is a sun letter, so the lam of the definite article assimilates to it in speech although it is still written.
The pairing of ra and zay is one of eight or so cases in which two Arabic letters share a single skeleton and are separated by pointing alone, and it belongs to the older layer of the alphabet rather than to the six letters Arabic added. Both ra and zay are inherited: zay descends from the Northwest Semitic zayin, the cognate of Hebrew zayin and Syriac zain, whose name has been reconstructed as meaning a sword or a weapon. That reconstruction belongs to the older linear script and not to Arabic. Its numeral value of seven is the value the inherited sequence assigns to the seventh letter, and it is one of the values on which the eastern and western reckonings of the abjad agree.
Zay closes hawwaz, the second of the eight mnemonic words by which the abjad sequence is remembered, and its numeral value of seven is fixed by that position. It is among the least frequent letters in running Arabic text, and unlike ra, the letter it is built from, it does not appear among the disjoined letters that stand at the head of certain suras.