I'd like to alter this definition slightly- "The practice of training people desired behaviors based on expectations, using a proactive approach and consequences when necessary".
I probably wouldn't have phrased it the way Webster did to begin with, but with some simple alterations, I think my idea comes across. To me, discipline is the big picture, not just the response. It incorporates who, what, when, why, and how. In order to discipline effectively, all of these questions need to be thought through, a plan devised, and consistency provided.