This is the 10464th most frequent Russian word.
ветряной
"Vетряной" means "windy" or "pertaining to wind."
The word 'ветряной' is used as an adjective describing the engine as being powered by wind.
Он построил большой ветряной двигатель.
He built a large wind-powered engine.
Here, 'ветряными' is the plural adjective form, describing the windmills.
Этот регион известен своими ветряными мельницами.
This region is famous for its windmills.
In this context, 'ветряной' metaphorically refers to someone's fickle or changeable nature.