Meaning of “runaway” - Learner’s Dictionary

runaway

adjective [ always before noun ] uk us /ˈrʌnəˌweɪ/
a runaway success/victory/winner, etc

something good that happens very quickly or easily

A runaway vehicle is moving away from somewhere without anyone controlling it:

a runaway car/train

(Definition of “runaway adjective” from the Cambridge Learner’s Dictionary © Cambridge University Press)