A literary source; the source from which a concept, piece of information, etc., derives.
Origin
Late 19th century; earliest use found in Frederic William Maitland (1850–1906), legal historian. From German Quelle spring, source (Old High German quella, Middle High German quelle), literary or historical source from German quellen to well up. Compare Old English cwylla, Middle Dutch quelle, Old Saxon quella (Middle Low German quelle), all in sense ‘spring, source’.