1620s, "Spanish legislative council," from Spanish and Portuguese junta "council, meeting, convention," from Medieval Latin iuncta "joint," from Latin iuncta, fem. past participle of iungere "to join together," from nasalized form of PIE root *yeug- "to join."
Meaning "political or military group in power" first recorded 1640s as junto (from confusion with Spanish nouns ending in -o), originally with reference to the Cabinet Council of Charles I. Modern spelling in this sense is from 1714; popularized 1808 in connection with private councils formed secretly across Spain to resist Napoleon. In English history, a group of leading Whigs in the reigns of William III and Queen Anne.