What does "let up" denote in "the rain/storm has let up so we can go out/drive back home"?
With a context lacking clarity, should it be understood as, "the [hard] rain/storm has lessened up to a light sprinkle/gentle rain (making it safe to go out, drive, use the Internet again, etc.)," or "the rain/storm has stopped and the weather is now calm"?
: to diminish, as in I hope this rain lets up a little soon. When the snow lets up so I can see, I will drive to the store. McGraw-Hill Dictionary of American Idioms and Phrasal Verbs
: to cease, stop entirely, as in The rain has let up so we can go out. [Late 1700s] The American Heritage® Dictionary of Idioms by Christine Ammer