'To let on' definitions:

Definition of 'To let on'

From: GCIDE

Let \Let\, v. i.
1. To forbear. [Obs.] --Bacon. [1913 Webster]
2. To be let or leased; as, the farm lets for $500 a year. See note under Let, v. t. [1913 Webster]
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.] [1913 Webster]