This is mainly an economics word. An expansionary policy tries to help a business or a whole country's economy grow — more government spending, lower taxes, easier loans. News and textbooks talk about expansionary fiscal policy (the government spends more or taxes less) and expansionary monetary policy (the central bank makes money easier to get). The opposite direction is contractionary: cooling things down. It is formal. You will meet it in economy news, not in everyday chat. Though actually, 'expansionary' names the aim of the policy, not a promise that growth will come; a plan can be expansionary and still fail.

擴張性的（經濟政策）。教科書說「擴張性財政／貨幣政策」；台灣新聞講貨幣時更常說「寬鬆」。