ballast - Dictionary definition and meaning for word ballast
ballast -- balance -- you are adding something to balance it or make it stable ( just as in weighing balance)
Divide it like--Bal(Balance)+Last(last long), adding weight to bring balance to something(as in weighing balance) or to make it stable that last long.
ballast = ball(imagine a heavy iron ball) + st(ability)
blast... to stop something from blasting away, put heavy substance on it..
Bal(Balance) + st(stability)>>> Adding something to balance or stabilize or support something..