What is "to let up"

Let \Let\, v. i.

1. To forbear. [Obs.]
   --Bacon.

2. To be let or leased; as, the farm lets for $500 a year. See note under Let, v. t.

   To let on, to tell; to tattle; to divulge something. [Low]

   To let up, to become less severe; to diminish; to cease; as, when the storm lets up. [Colloq.]