Quentin Trimble: Etym: From Latin for "fifth"; also the name for a type of French linen around the end of the 17th century.
Quidditch: The most popular sport in the wizarding world, combining, on the one hand, the fast-moving team action of soccer or basketball with, on the other hand, the injury rate of rugby and the vehicular technology arms race of Formula One.
Briefly, a game takes place on brooms between two teams, each consisting of three Chasers, two Beaters, a Keeper, and a Seeker, using three types of ball: a Quaffle, two Bludgers, and the Golden Snitch. For a full treatment of the subject, see Quidditch Through the Ages or Quidditch.com.
Quidditch Through the Ages: The definitive work on the history of Quidditch, available in a Muggle edition.
Quirrell: The last name of the teacher of Defense Against the Dark Arts in Harry's first year; revealed as a servant of Voldemort and killed in a confrontation with Harry.
Etym: Nickname for a troublemaker, from Middle English/Old French querel, meaning "complaint, accusation".