Definition of Allusion
In Volume 1, Book 1, Chapter 17, Merlin goes to see his teacher, Bleise. Malory does not fully characterize Bleise, who is a figure from older Arthurian lore, but rather alludes to him in a way that helps establish his own authority as a storyteller (in a rhetorical tactic called ethos):
And there [Merlin] told how Arthur and the two kings had sped at the great battle, and how it was ended, and told the names of every king and knight of worship that was there. And so Bleise wrote the battle word by word, as Merlin told him how it began, and by whom, and in likewise how it was ended, and who had the worse. All the battles that were done in Arthur’s days, Merlin did his master Bleise do write; also he did do write all the battles that every worthy knight did of Arthur’s court.
In Volume 1, Book 1, Chapter 27, Arthur follows Merlin's advice to have all the children born around May-Day killed because one of them will grow up to destroy Arthur. This incident alludes to two Biblical stories, and it foreshadows Arthur's downfall at the end of the Book:
Unlock with LitCharts A+Merlin told King Arthur that he that should destroy him should be born in May-day, wherefore he sent for them all, upon pain of death; and so there were found many lords’ sons, [...] and all were put in a ship to the sea, and some were four weeks old, and some less.
The book contains several allusions to Joseph of Arimathea. For example, in Volume 2, Book 13, Chapter 3, Galahad is introduced as the rightful occupant of the Siege Perilous because he is related to Joseph of Arimathea:
Unlock with LitCharts A+Then the old man said unto Arthur, ‘Sir, I bring here a young knight, the which is of kings’ lineage, and of the kindred of Joseph of Arimathea, whereby the marvels of this court, and of strange realms, shall be fully accomplished.’