When it first entered English in the late 16th century, fountainhead was used only in a literal sense—to refer to the source of a stream. By the 17th century, however, it was already beginning to be used figuratively in reference to any original or primary source. In his 1854 work Walden, Henry David Thoreau used the word in its figurative sense, while paying full homage to its literal meaning as well: "Morning air! If men will not drink of this at the fountainhead of the day, why, then, we must even bottle up some and sell it in the shops, for the benefit of those who have lost their subscription ticket to morning time in this world."