Source : Webster's Revised Unabridged Dictionary (1913)

Drill \Drill\, n.
   1. An instrument with an edged or pointed end used for making
      holes in hard substances; strictly, a tool that cuts with
      its end, by revolving, as in drilling metals, or by a
      succession of blows, as in drilling stone; also, a drill
      press.

   2. (Mil.) The act or exercise of training soldiers in the
      military art, as in the manual of arms, in the execution
      of evolutions, and the like; hence, diligent and strict
      instruction and exercise in the rudiments and methods of
      any business; a kind or method of military exercises; as,
      infantry drill; battalion drill; artillery drill.

   3. Any exercise, physical or mental, enforced with regularity
      and by constant repetition; as, a severe drill in Latin
      grammar.

   4. (Zo["o]l.) A marine gastropod, of several species, which
      kills oysters and other bivalves by drilling holes through
      the shell. The most destructive kind is {Urosalpinx
      cinerea}.

   {Bow drill}, {Breast drill}. See under {Bow}, {Breast}.

   {Cotter drill}, or {Traverse drill}, a machine tool for
      drilling slots.

   {Diamond drill}. See under {Diamond}.

   {Drill jig}. See under {Jig}.

   {Drill pin}, the pin in a lock which enters the hollow stem
      of the key.

   {Drill sergeant} (Mil.), a noncommissioned officer whose
      office it is to instruct soldiers as to their duties, and
      to train them to military exercises and evolutions.

   {Vertical drill}, a drill press.

Breast \Breast\ (br[e^]st), n. [OE. brest, breost, As.
   bre['o]st; akin to Icel. brj[=o]st, Sw. br["o]st, Dan. bryst,
   Goth. brusts, OS. briost, D. borst, G. brust.]
   1. The fore part of the body, between the neck and the belly;
      the chest; as, the breast of a man or of a horse.

   2. Either one of the protuberant glands, situated on the
      front of the chest or thorax in the female of man and of
      some other mammalia, in which milk is secreted for the
      nourishment of the young; a mamma; a teat.

            My brother, that sucked the breasts of my mother.
                                                  --Cant. viii.
                                                  1.

   3. Anything resembling the human breast, or bosom; the front
      or forward part of anything; as, a chimney breast; a plow
      breast; the breast of a hill.

            Mountains on whose barren breast The laboring clouds
            do often rest.                        --Milton.

   4. (Mining)
      (a) The face of a coal working.
      (b) The front of a furnace.

   5. The seat of consciousness; the repository of thought and
      self-consciousness, or of secrets; the seat of the
      affections and passions; the heart.

            He has a loyal breast.                --Shak.

   6. The power of singing; a musical voice; -- so called,
      probably, from the connection of the voice with the lungs,
      which lie within the breast. [Obs.]

            By my troth, the fool has an excellent breast.
                                                  --Shak.

   {Breast drill}, a portable drilling machine, provided with a
      breastplate, for forcing the drill against the work.

   {Breast pang}. See {Angina pectoris}, under {Angina}.

   {To make a clean breast}, to disclose the secrets which weigh
      upon one; to make full confession.

Source : WordNet®

breast drill
     n : a portable drill with a plate that is pressed against the
         chest to force the drill point into the work