Dewan (also known as diwan, sometimes spelled devan or divan) designated a powerful government official, minister, or ruler. A dewan was the head of a state institution of the same name (see Divan). Diwans belonged to the elite families in the history of Mughal and post-Mughal India and held high posts within the government.
The word is Persian in origin and was loaned into Arabic. The original meaning was "bundle (of written sheets)", hence "book", especially "book of accounts," and hence "office of accounts," "custom house," "council chamber". The meaning of the word, divan "long, cushioned seat" is due to such seats having been found along the walls in Middle Eastern council chambers. It is a common surname among Sikhs in Punjab. 
The divan of the Sublime Porte was the council or Cabinet of the state. In the Ottoman Empire, it consisted of the usually (except in the Sultan's presence) presiding Grand Vizier and other viziers, and occasionally the Janissary Ağa.
In Javanese and related languages, the cognate "dewan" is the standard word for council, as in the Dewan Perwakilan Rakyat or (Indonesia's Council of People's Representatives) and Dewan Negara (Senate of Malaysia).
Later, when most vassal states gained various degrees of self-determination, the finance — and/or chief minister and leader of many princely states (especially Muslim, but also many Hindu, including Baroda, Hyderabad, Mysore, Kochi, Travancore — referred to as Dalawa until 1811) became known as a dewan.
Exceptionally, a ruler was himself titled Dewan or a loftier variation, notably:
- in Beri-Bundelkhand
- in Dhurwai
- in Jaso (Jassu) and in Bandhora (which was split from the former c. 1750)
- in Khilchipur until 1873, then Rai Bahadur
- in Junagadh, where Shah Nawaz Bhutto was the prime minister of the former princley state.
- Diwan Sahib or Diwan Bahadur in Garrauli State
As a title used in various Early Modern Indian states, Diwan denoted the highest officials in the court after the king; the suffix -ji is added as a mark of respect in India. In the major Maratha states of Baroda (ruled by the Gaekwad), Gwalior (ruled by Scindias or Shinde), Indore (ruled by Holkar), and Nagpur (ruled by Bhonsle, but not from the Chhatrapati Shivaji family), the highest officer after the king was called the Diwan.
One of the examples – Shrimant Diwan/Rao Bahadur Atmaram Kulkarni, was the Diwan (Prime Minister) of Maratha Jamkhandi State. In the 19th century, the British Parliament established in British India a supreme court for revenue matters (non-criminal matters) named the "Sudder Dewanny Adawlut", which applied Hindu law.
Among Hindus and Sikhs of Punjab and Bengal
Diwan also became a surname of high-caste Hindus or Sikhs in the Punjab region.
There is also a community with the surname Diwan found in Chhattisgarh, near the Bilaspur and Janjgir-Champa regions. This is a Brahmin-Rajput community descendant from Deo Brahmin-Rajputs who migrated from Purvanchal in Uttar Pradesh. The males in this community take the title Dhar (eg. Mohan Dhar Diwan, a high-ranked member of Vishwa Hindu Parishad). They had a fight with the royal family of Ratanpur, defeated the king, and started ruling the Ratanpur estate.
Diwani in British India
After the Battle of Buxar, when Bengal was annexed by the East India Company in 1764, the Mughal Emperor granted the Company the Diwani (the right to collect revenue) in Bengal and Bihar in 1765. The term Diwani thus referred to British (fiscal) suzerainty over parts of India during the early British Raj.
Diwani in French India
In French India, one of its constituent colonies, Yanaon, had Zamindar and Diwan. They were active in its local and municipal administration during French rule. The Zamindar of Yanam was given a 4-gun salute by French counterparts.
- Zamindar — Manion Canacaya
- Diwan — Bouloussou Soubramaniam Sastroulou
- Sovereignty — French Colonial Empire
The document dated Bikram Samvat 1833 Bhadra Vadi 3 Roj 6 (i.e. Friday 2 August 1776), shows that Vamsharaj Pande and Swaroop Singh Karki had carried the title of Dewan (equivalent to Prime Minister) of the Kingdom of Nepal.
- Thangjam, Homen (Summer 2014). "Militarism, Human Rights, and Democracy in Northeast India". Kangla Lanpung. RK Sanatomba Memorial Trust,Imphal. VIII (II): 27–. ISSN 2321-2357.
- Campbell, Lawrence Dundas (ed), Asiatic Annual Register for 1802, or A View of the History of Hindustan and of the Politics, Commerce and Literature of Asia, London, J. Debrett, 1803, footnote pp.97-100, Miscellaneous Tracts 
- Definition per James Mill (1826): "Dewan, Duan: place of assembly. Native minister of the revenue department; and chief justice, in civil causes, within his jurisdiction; receiver-general of a province. The term is also used, to designate the principal revenue servant under a European collector, and even of a Zemindar. By this title, the East India Company are receivers-general of the revenues of Bengal, under a grant from the Great Mogul"..."Dewanny, Duannee: the office, or jurisdiction of a Dewan" (Mill, James, The History of British India, Vol. 1 (of 6), 3rd Edition, London, 1826, Glossary )
- Robb, Peter (2004). A History of India. Palgrave Macmillan. pp. 116–147. ISBN 978-0-333-69129-8. "Chapter 5: Early Modern India II: Company Raj", Metcalf, Barbara D.; Metcalf, Thomas R. (2006), A Concise History of Modern India, Cambridge University Press, pp. 56–91, ISBN 978-1-139-45887-0 "Chapter 3: The East India Company Raj, 1772-1850," Bose, Sugata; Jalal, Ayesha (2003). Modern South Asia: History, Culture, Political Economy (2nd ed.). Routledge. pp. 76–87. ISBN 0-415-30787-2. "Chapter 7: Company Raj and Indian Society 1757 to 1857, Reinvention and Reform of Tradition."
- Regmi 1975, p. 272.