Arabic term (edited): ������

Historically (by your reference to "tadwin" - writing in the state diwan, I assume you mean the Umayyad or Abbasid caliphate), such post holders were known as "secretaries" and not "clerks". Clerk is the modern meaning and is historically inaccurate as to their function and role in state administration.

http://www.witness-pioneer.org/vil/Articles/companion/15_uma...
Each province was under the charge of a Governor or Wali. Other officers at the provincial level were:
(1) Katib, or Chief Secretary;
(2) Katib-ud-Diwan; Secretary, Army

http://www1.muis.gov.sg/lectures/kazem-lec.doc
Under Umayyad, the head of diwan was called katib (secretary). According to Encyclopedia of Islam, both the idea and the word came from Iran.

Clerk and court clerk are more contemporary definitions. Hope that helps :-)