. . .the widespread use of what were called (dismissively, by truly learned folk) "inkhorn terms."
-- Simon Winchester, "Word Imperfect", The Atlantic Monthly, May 2001
In prison he wrote the De Consolatione Philosophiae, his most celebrated work and one of the most translated works in history; it was translated . . . by Elizabeth I into florid, inkhorn language.
-- The Oxford Companion to English Literature, s.v. "Boethius, Anicius Manlius Severinus (c. 475 - 525)."
Inkhorn derives from the name for the container formerly used (beginning in the 14th century) for holding ink, originally made from a real horn. Hence it came to refer to words that were being used by learned writers and scholars but which were unknown or rare in ordinary speech.