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.
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   2. Difficult, mentally or judicially; not easily apprehended,
      decided, or resolved; as a hard problem.
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            The hard causes they brought unto Moses. --Ex.
                                                  xviii. 26.
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            In which are some things hard to be understood. --2
                                                  Peter iii. 16.
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   3. Difficult to accomplish; full of obstacles; laborious;
      fatiguing; arduous; as, a hard task; a disease hard to
      cure.
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   4. Difficult to resist or control; powerful.
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            The stag was too hard for the horse.  --L'Estrange.
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            A power which will be always too hard for them.
                                                  --Addison.
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   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.
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            I never could drive a hard bargain.   --Burke.
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   6. Difficult to please or influence; stern; unyielding;
      obdurate; unsympathetic; unfeeling; cruel; as, a hard
      master; a hard heart; hard words; a hard character.
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   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.
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   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.
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   10. Wanting softness or smoothness of utterance; harsh; as, a
       hard tone.
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   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.
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   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.
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The Collaborative International Dictionary of English v.0.48:

Quahog \Qua"hog\, Quahaug \Qua"haug\, n. [Abbrev. fr.
   Narragansett Indian poqua[^u]hock.] (Zool.)
   An American market clam (Venus mercenaria). It is sold in
   large quantities, and is highly valued as food. Called also
   round clam, and hard clam.
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   Note: The name is also applied to other allied species, as
         Venus Mortoni of the Gulf of Mexico.
         [1913 Webster] Quaigh

WordNet (r) 3.0 (2006):

hard clam
    n 1: an edible American clam; the heavy shells were used as
         money by some American Indians [syn: quahog, quahaug,
         hard-shell clam, hard clam, round clam, Venus
         mercenaria, Mercenaria mercenaria]