Source : Webster's Revised Unabridged Dictionary (1913)

Lowering \Low"er*ing\, a.
   Dark and threatening; gloomy; sullen; as, lowering clouds or
   sky.

Lower \Low"er\, v. i. [imp. & p. p. {Lowered}; p. pr. & vb. n.
   {Lowering}.] [OE. lowren, luren; cf. D. loeren, LG. luren. G.
   lauern to lurk, to be on the watch, and E. leer, lurk.]
   1. To be dark, gloomy, and threatening, as clouds; to be
      covered with dark and threatening clouds, as the sky; to
      show threatening signs of approach, as a tempest.

            All the clouds that lowered upon our house. --Shak.

   2. To frown; to look sullen.

            But sullen discontent sat lowering on her face.
                                                  --Dryden.

Lower \Low"er\, v. t. [imp. & p. p. {Lowered}; p. pr. & vb. n.
   {Lowering}.] [From {Low}, a.]
   1. To let descend by its own weight, as something suspended;
      to let down; as, to lower a bucket into a well; to lower a
      sail or a boat; sometimes, to pull down; as, to lower a
      flag.

            Lowered softly with a threefold cord of love Down to
            a silent grave.                       --Tennyson.

   2. To reduce the height of; as, to lower a fence or wall; to
      lower a chimney or turret.

   3. To depress as to direction; as, to lower the aim of a gun;
      to make less elevated as to object; as, to lower one's
      ambition, aspirations, or hopes.

   4. To reduce the degree, intensity, strength, etc., of; as,
      to lower the temperature of anything; to lower one's
      vitality; to lower distilled liquors.

   5. To bring down; to humble; as, to lower one's pride.

   6. To reduce in value, amount, etc.; as, to lower the price
      of goods, the rate of interest, etc.

Source : WordNet®

lowering
     adj : darkened by clouds; "a heavy sky" [syn: {heavy}, {sullen}, {threatening}]

lowering
     n 1: the act of causing to become less
     2: the act of causing something to move to a lower level [syn:
        {letting down}]