Fountainhead is a word usually encountered in literary contexts that refers to the origin or source of something.

// Ragtime, popularized by such performers as Scott Joplin and Eubie Blake, is considered one of the musical fountainheads of jazz.

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“In Marbury, in 1803, Chief Justice John Marshall proclaimed, ‘It is emphatically the province and duty of the judicial department to say what the law is.’ There, the Supreme Court, for the first time, declared an act of Congress unconstitutional and ‘entirely void.’ Because the Court implied that its own authority to interpret the Constitution is superior to that of the other branches, the case is the fountainhead of judicial supremacy.” — Jeannie Suk Gersen, The New Yorker, 5 Jan. 2023

In Walden, widely considered Henry David Thoreau’s masterwork, the poet-philosopher extolled one major—nay, transcendent—perk of being an early bird: “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.” Thoreau was using fountainhead in its figurative sense—referring to morning as the “origin” of the day to follow—while also paying homage to its literal meaning, “the source of a stream” (the earliest sense of fountain being “a natural spring”). As someone who spent two years living, writing, and meditating in a cabin, Thoreau was nothing, after all, if not thorough.