The Collaborative International Dictionary of English v.0.48:

Hard \Hard\ (h[aum]rd), a. [Compar. Harder (-[~e]r); superl.
   Hardest.] [OE. hard, heard, AS. heard; akin to OS. & D.
   hard, G. hart, OHG. herti, harti, Icel. har[eth]r, Dan.
   haard, Sw. h[*a]rd, Goth. hardus, Gr. kraty`s strong,
   ka`rtos, kra`tos, strength, and also to E. -ard, as in
   coward, drunkard, -crat, -cracy in autocrat, democracy; cf.
   Skr. kratu strength, k[.r] to do, make. Cf. Hardy.]
   1. Not easily penetrated, cut, or separated into parts; not
      yielding to pressure; firm; solid; compact; -- applied to
      material bodies, and opposed to soft; as, hard wood;
      hard flesh; a hard apple.
      [1913 Webster]

   2. Difficult, mentally or judicially; not easily apprehended,
      decided, or resolved; as a hard problem.
      [1913 Webster]

            The hard causes they brought unto Moses. --Ex.
                                                  xviii. 26.
      [1913 Webster]

            In which are some things hard to be understood. --2
                                                  Peter iii. 16.
      [1913 Webster]

   3. Difficult to accomplish; full of obstacles; laborious;
      fatiguing; arduous; as, a hard task; a disease hard to
      cure.
      [1913 Webster]

   4. Difficult to resist or control; powerful.
      [1913 Webster]

            The stag was too hard for the horse.  --L'Estrange.
      [1913 Webster]

            A power which will be always too hard for them.
                                                  --Addison.
      [1913 Webster]

   5. Difficult to bear or endure; not easy to put up with or
      consent to; hence, severe; rigorous; oppressive;
      distressing; unjust; grasping; as, a hard lot; hard times;
      hard fare; a hard winter; hard conditions or terms.
      [1913 Webster]

            I never could drive a hard bargain.   --Burke.
      [1913 Webster]

   6. Difficult to please or influence; stern; unyielding;
      obdurate; unsympathetic; unfeeling; cruel; as, a hard
      master; a hard heart; hard words; a hard character.
      [1913 Webster]

   7. Not easy or agreeable to the taste; harsh; stiff; rigid;
      ungraceful; repelling; as, a hard style.
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            Figures harder than even the marble itself.
                                                  --Dryden.
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   8. Rough; acid; sour, as liquors; as, hard cider.
      [1913 Webster]

   9. (Pron.) Abrupt or explosive in utterance; not aspirated,
      sibilated, or pronounced with a gradual change of the
      organs from one position to another; -- said of certain
      consonants, as c in came, and g in go, as distinguished
      from the same letters in center, general, etc.
      [1913 Webster]

   10. Wanting softness or smoothness of utterance; harsh; as, a
       hard tone.
       [1913 Webster]

   11. (Painting)
       (a) Rigid in the drawing or distribution of the figures;
           formal; lacking grace of composition.
       (b) Having disagreeable and abrupt contrasts in the
           coloring or light and shade.
           [1913 Webster]

   Hard cancer, Hard case, etc. See under Cancer, Case,
      etc.

   Hard clam, or Hard-shelled clam (Zool.), the quahog.

   Hard coal, anthracite, as distinguished from bituminous
      coal (soft coal).

   Hard and fast. (Naut.) See under Fast.

   Hard finish (Arch.), a smooth finishing coat of hard fine
      plaster applied to the surface of rough plastering.

   Hard lines, hardship; difficult conditions.

   Hard money, coin or specie, as distinguished from paper
      money.

   Hard oyster (Zool.), the northern native oyster. [Local, U.
      S.]

   Hard pan, the hard stratum of earth lying beneath the soil;
      hence, figuratively, the firm, substantial, fundamental
      part or quality of anything; as, the hard pan of
      character, of a matter in dispute, etc. See Pan.

   Hard rubber. See under Rubber.

   Hard solder. See under Solder.

   Hard water, water, which contains lime or some mineral
      substance rendering it unfit for washing. See Hardness,
      3.

   Hard wood, wood of a solid or hard texture; as walnut, oak,
      ash, box, and the like, in distinction from pine, poplar,
      hemlock, etc.

   In hard condition, in excellent condition for racing;
      having firm muscles; -- said of race horses.

   Syn: Solid; arduous; powerful; trying; unyielding; stubborn;
        stern; flinty; unfeeling; harsh; difficult; severe;
        obdurate; rigid. See Solid, and Arduous.
        [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Rubber \Rub"ber\, n.
   1. One who, or that which, rubs. Specifically:
      (a) An instrument or thing used in rubbing, polishing, or
          cleaning.
      (b) A coarse file, or the rough part of a file.
      (c) A whetstone; a rubstone.
      (d) An eraser, usually made of caoutchouc or a synthetic
          rubber[4].
      (e) The cushion of an electrical machine.
      (f) One who performs massage, especially in a Turkish
          bath.
      (g) Something that chafes or annoys; hence, something that
          grates on the feelings; a sarcasm; a rub. --Thackeray.
          [1913 Webster]

   2. In some games, as bridge or whist, the odd game, as the
      third or the fifth, which decides the winner when there is
      a tie between the players; as, to play the rubber; also, a
      contest determined by the winning of two out of three
      games; as, to play a rubber of whist. --Beaconsfield. "A
      rubber of cribbage." --Dickens.
      [1913 Webster]

   3. India rubber; caoutchouc; gum elastic; -- also called
      natural rubber.
      [1913 Webster +PJC]

   4. Any substance, whether natural or synthetic, resembling
      India rubber with respect to its elasticity[1].
      [PJC]

   5. A low-cut overshoe made of natural or synthetic rubber[4],
      serving to keep the feet and shoes dry when walking in the
      rain or on a wet surface; -- usually used in the plural.
      [1913 Webster]

   6. A condom. [Slang]
      [PJC]

   Antimony rubber, an elastic durable variety of vulcanized
      caoutchouc of a red color. It contains antimony sulphide
      as an important constituent.

   Hard rubber, a kind of vulcanized caoutchouc which nearly
      resembles horn in texture, rigidity, etc.

   India rubber, caoutchouc. See Caoutchouc.

   Rubber cloth, cloth covered with caoutchouc for excluding
      water or moisture.

   Rubber dam (Dentistry), a shield of thin sheet rubber
      clasped around a tooth to exclude saliva from the tooth.
      [1913 Webster]

WordNet (r) 3.0 (2006):

hard rubber
    n 1: a hard nonresilient rubber formed by vulcanizing natural
         rubber [syn: hard rubber, vulcanite, ebonite]