DeadHead Definitions
"I made a mixture with clear water, and filtered it to take away the dead head of it. " (Husbandry & Gardening, 1707)
"When castings are required to be particularly solid, they are generally made with what is called a dead head." (English Mechanic, 1869)
"Dead head, a kind of dolphin or stout post on a quay head to make hawsers fast to; a rough block of wood used as an anchor buoy." (Smyth's Sailor's Wordbook, 1867)
"Dead head: One who returns without a load. " (Webster's Collegiate Dictionary)
"The forest covered slopes of Deadhead Hill, whose summit rim is always outlined in black by the crowding figures of the deadheads assembled to see the game. " (0. D. von Engeln, At Cornell, 1909)
"As I had never experienced the blessed privilege of deadheadism, I could not naturally miss the opportunity of enjoying so new a sensation." (N. Y Tribune, 1857)
"In Pittsfield, recently, he is reported to have advertised that he could furnish a free pass to glory, but very few of the unrighteous population seems anxious to be dead-headed on this train." (N. Y. Tribune, 1871)
"He had been dead-headed into the world some fifty years ago, and had sat with his hands in his pockets staring at the show ever since." (Oliver Wendel Holmes, Elsie V ii, 1860)
(Quotes from Oxford & Webster's dictionaries)
Found in a reprinting of the last deadhead newsletter published by the Grateful Dead in 1980. The word seems to get around.