The Collaborative International Dictionary of English v.0.48:

Duck \Duck\, v. t. [imp. & p. p. Ducked; p. pr. & vb. n.
   Ducking.] [OE. duken, douken, to dive; akin to D. duiken,
   OHG. t?hhan, MHG. tucken, t["u]cken, t?chen, G. tuchen. Cf.
   5th Duck.]
   1. To thrust or plunge under water or other liquid and
      suddenly withdraw.
      [1913 Webster]

            Adams, after ducking the squire twice or thrice,
            leaped out of the tub.                --Fielding.
      [1913 Webster]

   2. To plunge the head of under water, immediately withdrawing
      it; as, duck the boy.
      [1913 Webster]

   3. To bow; to bob down; to move quickly with a downward
      motion. " Will duck his head aside." --Swift.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Ducking \Duck"ing\,
   n. & a., from Duck, v. t. & i.
   [1913 Webster]

   Ducking stool, a stool or chair in which common scolds were
      formerly tied, and plunged into water, as a punishment.
      See Cucking stool. The practice of ducking began in the
      latter part of the 15th century, and prevailed until the
      early part of the 18th, and occasionally as late as the
      19th century. --Blackstone. Chambers.
      [1913 Webster]

WordNet (r) 3.0 (2006):

ducking
    n 1: hunting ducks [syn: ducking, duck hunting]
    2: the act of wetting something by submerging it [syn:
       submersion, immersion, ducking, dousing]