Adventure, Historical Fiction
"The Knight's Tale" is a work of fiction set in a time period much earlier than the one in which it's written. (The story is told in medieval England, but it's about ancient Greece.) This makes it a medieval version of what, today, we might call historical fiction. Just like our historical fiction, "The Knight's Tale" draws upon some of the attitudes it imagines those historical figures might have had, like worship of Greek gods, beliefs surrounding burial of the dead, and ancient Greek philosophies like Stoicism and Platonism. (See "Setting" for more on that.)
Just like our historical fiction, "The Knight's Tale" also contains many anachronisms – attitudes which, if we thought harder about it, we'd realize probably don't belong to the setting of the story. They come from the time the story was written, rather than the historical time in which it is set. In "The Knight's Tale," attitudes like chivalry and courtly love are anachronistic in a story about ancient Greece (as is the jousting competition…).
We can also consider "The Knight's Tale" an adventure because it includes lots of acts of physical derring-do, like jousts, duels, and battles. Medieval adventures tend to include disguise and mistaken identity, too. We see this in "The Knight's Tale" when Arcite disguises himself as a servant and Palamon fails to recognize him immediately.