The Latin adjective desultorius was used by the ancients to refer to a circus performer (called a desultor) whose trick was to leap from horse to horse without stopping. It makes sense, then, that someone or something desultory "jumps" from one thing to another. (Desultor and desultorius, by the way, come from the Latin verb salire, meaning "to leap.") A desultory conversation leaps from one topic to another and doesn't have a distinct point or direction. A desultory student skips from one subject to another without applying serious effort to any particular one. A desultory comment is a digressive one that jumps away from the topic at hand. And a desultory performance is one resulting from an implied lack of steady, focused effort.