William Nassau Lees (1825–1889) was a British Army officer in India, known as an orientalist.
The fourth son of Sir Harcourt Lees, bart., he was born on 26 February 1825, and educated at Nut Grove and at Trinity College, Dublin, but took no degree. He was appointed to a Bengal cadetship in 1846, and was posted to the 42nd Regiment of Bengal Native Infantry as ensign in March 1846. He became lieutenant in July 1853, captain in September 1858, major in June 1865, lieutenant-colonel in 1868, colonel in 1876, and major-general in 1885, having been placed on the supernumerary list in 1884.
Lees was for some years principal of the Calcutta Madrasa, where he was also professor of law, logic, literature, and mathematics. He was secretary to Fort William College, Persian translator to the government, and government examiner in Arabic, Persian, and Urdu for all branches of the service; and for some years part proprietor of the Times of India. In 1857 Trinity College, Dublin conferred on him the honorary degree of LL.D., and he was also a Ph.D. of Berlin. He became a member of the Royal Asiatic Society in 1872.
A conservative in politics, Lees twice sought to enter parliament, but without success. He died at his residence in Grosvenor Street, London, on 9 March 1889, aged 64.
In 1853, when still an ensign, Lees brought out an edition of the Arabic Fatúh'sh-Shám attributed to al-Waqidi, an account of the Muslim conquest of Syria; and edited or co-edited various Indian works. He was noted for his edition of the Commentary (Al-Kashshaaf) of Al-Zamakhshari, an exegesis of the Koran. In Persian, his Nafahatu l'Uns of Jámí (an account of saints and Sufis, modernised from an older chronicle), one of the foundational works for the Western study of Sufism, and the Vis u Rámin, based on a Páhlévi romance of Vis and Rāmin, were well known.