Definition of "sachem"

Planted with their broad ends on the deck, a circle of these slabs laced together, mutually sloped towards each other, and at the apex united in a tufted point, where the loose hairy fibres waved to and fro like the top-knot on some old Pottowottamie Sachem’s head.

1851 November 14, Herman Melville, chapter XVI, in Moby-Dick; or, The Whale, 1st American edition, New York, N.Y.: Harper & Brothers; London: Richard Bentley

If a sachem was too harsh, a tribesman might leave and join another tribe.

1983, Howard S. Russell, Indian New England Before the Mayflower, page 19

The society elects annually thirteen sachems, which represent the original thirteen States. […] The other officers of the society are a Secretary, Treasurer, Sagamore, and Wiskinkie.

1865, R. G. Horton, “The History of Tammany Society, or, Columbian Order. Chapter V. From 1834 to 1840.”, in D. T. Valentine, Manual of the Corporation of the City of New York, New York, N.Y.: Edmund Jones & Co. [for the Common Council], page 876

Aboriginal titles were adopted and the head of each tribe was called a sachem. […] Its proprietor, Abraham Martling, was elected a sachem on several occasions and members of Tammany were often called Martling Men.

1983, Virgil W. Peterson, The Mob: 200 Years of Organized Crime in New York, page 4