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Webster 1913 Edition

Noun.

A strap placed across a man’s forehead to assist him in carrying a pack on his back.

[Local, U. S.]

Bartlett.

See also: tump line

Using a tumpline

tumpline ‎(plural tumplines)

A strap used to carry objects tied to its ends by placing the broadened or cushioned middle of the strap over the head just above the forehead.
- 1918, Rex Ellingwood Beach, The Winds of Chance, ch. 2:
  The speaker slipped his arms into his pack-harness and adjusted the tumpline to his forehead preparatory to rising.