Ghayn is the nineteenth letter of the modern Arabic order. It is the ayn skeleton with a single dot placed above it, and like ayn it joins on both sides and takes four markedly different shapes according to position. It is a moon letter, so the lam of the definite article is pronounced before it.
Its sound is a voiced velar fricative, a rasping g made without full closure, close to the r of Parisian French and to the g of some Dutch. It is the voiced counterpart of kha, and both belong to the group of throat letters, at the end of that group nearest the mouth.
Ghayn is the last of the six letters Arabic added to the alphabet it inherited, and that fact fixes its numeral value. The abjad reckoning assigns values by position in the inherited twenty-two letter sequence, from one to four hundred; the six additions were appended after it and took the six remaining values, five hundred to one thousand, in the order in which they were appended. Ghayn came last and therefore carries one thousand, the highest value in the system.
That has consequences beyond arithmetic. Because the largest number in the abjad belongs to a letter with no ancient pedigree, chronograms and letter calculations weight most heavily a letter the older Semitic alphabets never had. As one of the added letters, ghayn has no inherited name and no reconstructed pictographic sense.