The Collaborative International Dictionary of English v.0.48:

Herb \Herb\ ([~e]rb or h[~e]rb; 277), n. [OE. herbe, erbe, OF.
   herbe, erbe, F. herbe, L. herba; perh. akin to Gr. forbh`
   food, pasture, fe`rbein to feed.]
   1. A plant whose stem does not become woody and permanent,
      but dies, at least down to the ground, after flowering.
      [1913 Webster]

   Note: Annual herbs live but one season; biennial herbs flower
         the second season, and then die; perennial herbs
         produce new stems year after year.
         [1913 Webster]

   2. Grass; herbage.
      [1913 Webster]

            And flocks
            Grazing the tender herb.              --Milton.
      [1913 Webster]

   Herb bennet. (Bot.) See Bennet.

   Herb Christopher (Bot.), an herb (Act[ae]a spicata),
      whose root is used in nervous diseases; the baneberry. The
      name is occasionally given to other plants, as the royal
      fern, the wood betony, etc.

   Herb Gerard (Bot.), the goutweed; -- so called in honor of
      St. Gerard, who used to be invoked against the gout. --Dr.
      Prior.

   Herb grace, or Herb of grace. (Bot.) See Rue.

   Herb Margaret (Bot.), the daisy. See Marguerite.

   Herb Paris (Bot.), an Old World plant related to the
      trillium (Paris quadrifolia), commonly reputed
      poisonous.

   Herb Robert (Bot.), a species of Geranium (Geranium
      Robertianum.)
      [1913 Webster]

WordNet (r) 3.0 (2006):

herb
    n 1: a plant lacking a permanent woody stem; many are flowering
         garden plants or potherbs; some having medicinal
         properties; some are pests [syn: herb, herbaceous
         plant]
    2: aromatic potherb used in cookery for its savory qualities

Moby Thesaurus II by Grady Ward, 1.0:

140 Moby Thesaurus words for "herb":
   Cretan dittany, algae, angelica, autophyte, balm, balsam, basil,
   bean, belladonna, boneset, borage, bracken, brown algae,
   burning bush, calendula, caraway, cardamom, castor-oil plant,
   chervil, chicory, climber, clover, conferva, confervoid, coriander,
   creeper, deadly nightshade, death camas, diatom, dill, dittany,
   drops, drug, electuary, elixir, ethical drug, fennel, fern,
   feverroot, figwort, fruits and vegetables, fucus, fungus,
   gas plant, generic name, ginseng, grapevine, green algae, gulfweed,
   hemp, henbane, herbs, heterophyte, horehound, hyssop, inhalant,
   ivy, kelp, legume, lentil, liana, lichen, lincture, linctus,
   liverwort, mandrake, marijuana, marjoram, materia medica, mayapple,
   medicament, medication, medicinal, medicinal herbs, medicine, mint,
   mixture, mold, monkshood, moss, mullein, mushroom, mustard,
   nonprescription drug, officinal, oregano, origanum, parasite,
   parasitic plant, parsley, patent medicine, pea, peppermint,
   perthophyte, pharmacon, physic, phytoplankton, planktonic algae,
   plant families, powder, preparation, prescription drug,
   proprietary, proprietary medicine, proprietary name, puffball,
   pulse, red algae, rockweed, rosemary, rue, rust, sage, saprophyte,
   sargasso, sargassum, savory, sea lentil, sea moss, sea wrack,
   seaweed, simples, smut, sorrel, spearmint, succulent,
   sweet woodruff, syrup, tansy, tarragon, theraputant, thyme, tisane,
   toadstool, tobacco, vegetable remedies, vetch, vine, wort, wrack



Easton's 1897 Bible Dictionary:

Herb
   (1.) Heb. 'eseb, any green plant; herbage (Gen. 1:11, 12, 29,
   30; 2:5; 3:18, etc.); comprehending vegetables and all green
   herbage (Amos 7:1, 2).

     (2.) _Yarak_, green; any green thing; foliage of trees (2
   Kings 19:26; Ps. 37:2); a plant; herb (Deut. 11:10).

     (3.) _Or_, meaning "light" In Isa. 26:19 it means "green
   herbs;" in 2 Kings 4:39 probably the fruit of some plant.

     (4.) _Merorim_, plural, "bitter herbs," eaten by the
   Israelites at the Passover (Ex. 12:8; Num. 9:11). They were
   bitter plants of various sorts, and referred symbolically to the
   oppression in Egypt.