nadir [Arab.,=opposite], in astronomy, the point on the celestial sphere directly opposite the zenith, i.e., directly beneath the observer.

Nadir Shah or Nader Shah, 1688-1747, shah of Iran (1736-47), sometimes considered the last of the great Asian conquerors. He was a member of the Afshar tribe. Although taken prisoner by the Uzbeks while he was still a child, he escaped and entered the service of the governor of Khorasan. There he earned a reputation for bravery. He then entered the service of Tahmasp, the son of Shah Sultan Husayn, who was asserting his claims against the Afghans under Mahmud, who had usurped the Persian throne. Nadir took the name Tahmasp Kuli Khan [Tahmasp's slave] and proceeded to win a series of battles against the Afghans. Decisively beaten, they retired to Kandahar, and Tahmasp was restored to the rule over Iran. Nadir, however, was the powerful figure of the realm. He warred against the Turks successfully, and when the shah turned victory to disaster by a conciliatory peace, Nadir in 1732 deposed him. Tahmasp's infant son Abbas III was placed on the throne with Nadir as regent. The conquests continued, and the western boundary was restored to what it had been before the Afghan invasions. In 1736 Nadir deposed Abbas and himself became shah, thus ending the rule of the Safavid dynasty. He attempted to weld Iran and the Ottoman Empire by unifying the Shiites and Sunnis. This led to much dissatisfaction in Shiite Iran, and the plan was discarded. In 1738-39 Nadir invaded Mughal India. He was brilliantly successful, taking and sacking Delhi and Lahore and carrying off vast treasure, including the Koh-i-noor diamond and the Peacock Throne. He also continued his conquests in other directions. Bukhara was subdued, and the limits of Iran were extended to the greatest that they had been since the days of the Sassanids. War with the Turks occupied his attention from 1743 to 1746. Nadir's later years were darkened by a turn toward tyranny, suspicion, and greed. So much did he fear opposition that he had his own son blinded. In 1747, during a campaign against rebellious Kurds, Nadir Shah was assassinated by officers of his own guard. Although the dynasty he founded, the Afshar dynasty (1736-49), was short-lived, Nadir is generally regarded as one of the greatest of all rulers of Persia.

(born Oct. 22, 1688, Kobhan, Ssubdotafavid Iran—died June 1747, near Fathsubdotābād) Iranian conqueror and ruler. Originally a bandit of the Turkish Afshar tribes, he helped restore Tsubdotahmāsp II of the Ssubdotafavid dynasty to Iran's throne, defeating the Ghilzay Afghan usurper Mahsubdotmūd. He later deposed Tsubdotahmāsp II to place the latter's infant son on the throne; he made himself regent, then deposed the son and took the throne himself in 1736. He engaged in constant warfare with his neighbours, enlarging his empire from the Indus River to the Caucasus Mountains. Suspicious of those around him and capriciously cruel, he was assassinated by his own troops.

Learn more about Nādir Shāh with a free trial on Britannica.com.