The history of oudh as we know it today. عود as it is written in Arabic consists of the followings letter 'Ain ع followed by Waowو and ending with a Daal د . The last letter of the word Oudh is a Daal and this where the majority of the issues in the transliteration takes place. It requires a detailed understanding of Arabic Phonetics to be able to transliterate the letter correctly into English or any other language. د Daal has 6 Sifaat(qualities) : Jahr(vocalized), Shiddah(Strengthened), Istifal (Flat), Infittaah(opening), Ismat (pressing on the point of articulation) and Qalqalah, the last Sifah(quality) is the one that requires the most attention. Qalqalah is like a bounce of the sound or a shift/move of it, in the Arabic Language 5 letters have this quality associated with them ق ط ب ج د. Qalqalah is of two types, Kubra and Sughra, Major and Minor. The Minor Qalqalah takes place when one of the five letters has a Sukoon (no Harakah) in the middle of the word. In the word عود it is a Qalqalah Kubra because the د Daal is at the end of the word, which in common Arabic people will generally stop on. Which means the bounce is strong. Therefore the reason the h must exist is to differentiates it from the English letter d. Even if we consider the instances in the English language where D is more pronounced than normal such as in "Word", it is not the same as د Daal in عود, as that requires a clear bounce of the letter. Another point to note Dhaal does not have the Sifah of Hams and Rikhwah, which would allow flow of the breath, so the h is not for flowing of the breath but for the intensity of the bounce on the Daal. I had to address this publicly because it was brought to my attention (as a vendor who spells oudh with the h) that our brother Ensar@Gaharu was making some comments about Oud and Oudh. Another way we could look at it is, Oud is the modern Tom Ford, Armani, Lynx Oud Wood and Dark Vanilla way of spelling it and Oudh is Al Kindi, Ibn Baytaar and Al Azdi heritage enriched and vintaged oudhs. It is fairly simple for someone with a lot of tradition there is a reason behind every little detail in our Heritage, and the above is one such example.