What is "closet sin"

Closet \Clos"et\, n. [OF. closet little inclosure, dim. of clos. See Close an inclosure.]

1. A small room or apartment for retirement; a room for privacy.

   A chair-lumbered closet, just twelve feet by nine.
   --Goldsmith.

   When thou prayest, enter into thy closet.
   --Matt. vi. 6.

2. A small apartment, or recess in the side of a room, for household utensils, clothing, etc.
   --Dryden.

   Closet sin, sin commited in privacy.
   --Bp. Hall.