What is "to bite the thumb at"

Bite \Bite\ (b[imac]t), v. t. [imp. Bit (b[i^]t); p. p. Bitten (b[i^]t"t'n), Bit; p. pr. & vb. n. Biting.] [OE. biten, AS. b[=i]tan; akin to D. bijten, OS. b[=i]tan, OHG. b[=i]zan, G. beissen, Goth. beitan, Icel. b[=i]ta, Sw. bita, Dan. bide, L. findere to cleave, Skr. bhid to cleave.

1. To seize with the teeth, so that they enter or nip the thing seized; to lacerate, crush, or wound with the teeth; as, to bite an apple; to bite a crust; the dog bit a man.

   Such smiling rogues as these, Like rats, oft bite the holy cords atwain.
   --Shak.

2. To puncture, abrade, or sting with an organ (of some insects) used in taking food.

3. To cause sharp pain, or smarting, to; to hurt or injure, in a literal or a figurative sense; as, pepper bites the mouth. ``Frosts do bite the meads.''
   --Shak.

4. To cheat; to trick; to take in. [Colloq.]
   --Pope.

5. To take hold of; to hold fast; to adhere to; as, the anchor bites the ground.

   The last screw of the rack having been turned so often that its purchase crumbled, . . . it turned and turned with nothing to bite.
   --Dickens.

   To bite the dust, To bite the ground, to fall in the agonies of death; as, he made his enemy bite the dust.

   To bite in (Etching), to corrode or eat into metallic plates by means of an acid.

   To bite the thumb at (any one), formerly a mark of contempt, designed to provoke a quarrel; to defy. ``Do you bite your thumb at us?''
   --Shak.

   To bite the tongue, to keep silence.
   --Shak.