Ordinal Decades
When talking about milestones like a "twentieth celebration" or a "fiftieth anniversary," Arabic uses the exact same words as the cardinal tens (20, 30, 40, up to 90). To turn them into ordinal numbers (20th, 30th, 40th), simply add the definite article الـ.
These ordinal decades act as adjectives and match the case of the noun they describe. They decline using the sound masculine plural endings: ـون for the nominative case, and ـين for the accusative and genitive cases.
Importantly, ordinal decades do not change for gender. They keep their sound masculine plural form whether modifying a masculine noun (like احتفال) or a feminine noun (like ذكرى).
| The twentieth celebration of the institution is a glorious culmination. | الاحتفال العشرون للمؤسسة تتويج مجيد.al-ihtifâlu al-'ishrûna lil-mu'assasati tatwîjun majîd |
| The fiftieth anniversary is a culmination of a long history. | الذكرى الخمسون تتويج لتاريخ طويل.adhdhikrâ alkhamsûna tatwîjun litârîkhin tawîlin. |
Changing Case in Context
When a milestone functions as the object of a verb (accusative) or follows a preposition (genitive), the ordinal decade shifts to its oblique form ending in ـين.
| The prestigious university itself organized its thirtieth jubilee. | نظمت الجامعة المرموقة نفسها يوبيلها الثلاثين.nazzamati l-jâmi'atu l-marmûqatu nafsuhâ yûbîlahâ th-thalâthîn |
| We attended the glorious celebration of the twentieth anniversary of the foundation of the leading institution. | حضرنا الاحتفال المجيد بالذكرى العشرين لتأسيس المؤسسة الرائدة.haḍarnâ al-ihtifâla al-majîda bidh-dhikrâ al-ishrîna lita'sîsi al-mu'assasati ar-râ'idah |
| The professor published a book in commemoration of the fortieth anniversary of the institution. | نشرت الأستاذة كتابا تخليدا للذكرى الأربعين للمؤسسة.nasharati l-ustâdhatu kitâban takhlîdan lildhikra l-arba'îna lilmu'assasati. |