The five nouns

Five nouns show their case with a long vowel when a possessor follows: أب, أخ, حم, فم and ذو. The ending is و in the nominative, ا in the accusative and ي in the genitive.

Subject: جاء أبوك. Object: رأيت أباك. After a preposition or in an إضافة: سلمت على أبيك, بيت أخيك.

With my, all three become أبي and أخي. ذو, meaning having, always takes a noun after it: رجل ذو خبرة, قابلت رجلا ذا خبرة.