A Hundred and One Rules in Arabic Grammar!
- Long vowel to a Diphthong. ==============================
If any of the two long vowelو , ا ** ** is proceeded by the short vowel**–َ** ** ** , the long vowel changes its character to a diphthong:
uu ---> ou دَور ، دور
ii ---> ei **دَين ** ** ** ، دين