8/3/2008 found through at Merriam Webster

divagate: to wander or stray from a course or subject : digress

Not wanting to leave enough time for a quiz at the end of the lecture, Professor Srobitol’s students asked questions about birdwatching in the hopes that he would divagate from the top of supply-side economics and instead talk to them about the airspeed velocity of an unladen swallow.