As an adjective:
* The runaway train careened down the tracks, its brakes failing.
* She wrote a runaway bestseller that topped the charts for weeks.
* The runaway horse galloped through the field, its rider nowhere in sight.
As a noun:
* The runaway from the prison was caught by the police after three days.
* He was a runaway from a troubled home, seeking a new life.
* The runaway success of the company surprised even its founders.
As a verb:
* The prisoners tried to runaway but were quickly apprehended.
* Her imagination ranaway with her, creating elaborate stories in her mind.
* The car ranaway down the hill, gathering speed as it went.
As part of a phrase:
* He was a runaway success.
* The runaway leader in the race was quickly catching up.
* The runaway bride disappeared without a trace.