单凭猜测(或记忆);信口地;不假思索地
牛津电影里 100%
just guessing or using your memory, without taking time to think carefully or check the facts
Well, this is just off the top of my head, but, uh...
I was just thinking off the top of my head.
释义来自《牛津高阶英汉双解词典》第 9 版