mid-15c., "protraction, delay," verbal noun from train (v.). From 1540s as "discipline and instruction to develop powers or skills;" 1786 as "exercise to improve bodily vigor." Training wheels as an attachment to a bicycle is from 1953.
Training is the development of the mind or character or both, or some faculty, at some length, by exercise, as a soldier is trained or drilled. Discipline is essentially the same as training, but more severe. [Century Dictionary]