To let drive or fly, to discharge with violence, as a blow, an arrow, or stone. See under Drive, and Fly.

To let in or into.
   (a) To permit or suffer to enter; to admit.
   (b) To insert, or imbed, as a piece of wood, in a recess formed in a surface for the purpose. To let loose, to remove restraint from; to permit to wander at large.

To let off.
   (a) To discharge; to let fly, as an arrow; to fire the charge of, as a gun.
   (b) To release, as from an engagement or obligation. [Colloq.]

To let out.
   (a) To allow to go forth; as, to let out a prisoner.
   (b) To extend or loosen, as the folds of a garment; to enlarge; to suffer to run out, as a cord.
   (c) To lease; to give out for performance by contract, as a job.
   (d) To divulge.

To let slide, to let go; to cease to care for. [Colloq.]

`` Let the world slide.'' --Shak.

Source: Webster's Revised Unabridged Dictionary (1913)