The Collaborative International Dictionary of English v.0.48:

Marrow \Mar"row\, v. t. [imp. & p. p. Marrowed; p. pr. & vb.
   n. Marrowing.]
   To fill with, or as with, marrow or fat; to glut.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Marrow \Mar"row\, n. [OE. marou, mary, maruh, AS. mearg, mearh;
   akin to OS. marg, D. merg, G. Mark, OHG. marg, marag, Icel.
   mergr, Sw. merg, Dan. marv, Skr. majjan; cf. Skr. majj to
   sink, L. mergere. [root]274 Cf. Merge.]
   [1913 Webster]
   1. (Anat.) The tissue which fills the cavities of most bones;
      the medulla. In the larger cavities it is commonly very
      fatty, but in the smaller cavities it is much less fatty,
      and red or reddish in color.
      [1913 Webster]

   2. The essence; the best part.
      [1913 Webster]

            It takes from our achievements . . .
            The pith and marrow of our attribute. --Shak.
      [1913 Webster]

   3. [OE. maru, maro; -- perh. a different word; cf. Gael.
      maraon together.] One of a pair; a match; a companion; an
      intimate associate. [Scot.]
      [1913 Webster]

            Chopping and changing I can not commend,
            With thief or his marrow, for fear of ill end.
                                                  --Tusser.
      [1913 Webster]

   Marrow squash (Bot.), a name given to several varieties of
      squash, esp. to the Boston marrow, an ovoid fruit,
      pointed at both ends, and with reddish yellow flesh, and
      to the vegetable marrow, a variety of an ovoid form, and
      having a soft texture and fine grain resembling marrow.

   Spinal marrow. (Anat.) See Spinal cord, under Spinal.
      [1913 Webster]

WordNet (r) 3.0 (2006):

marrow
    n 1: the fatty network of connective tissue that fills the
         cavities of bones [syn: marrow, bone marrow]
    2: any of various squash plants grown for their elongated fruit
       with smooth dark green skin and whitish flesh [syn: marrow,
       marrow squash, vegetable marrow]
    3: very tender and very nutritious tissue from marrowbones [syn:
       marrow, bone marrow]
    4: large elongated squash with creamy to deep green skins [syn:
       marrow, vegetable marrow]
    5: the choicest or most essential or most vital part of some
       idea or experience; "the gist of the prosecutor's argument";
       "the heart and soul of the Republican Party"; "the nub of the
       story" [syn: kernel, substance, core, center,
       centre, essence, gist, heart, heart and soul,
       inwardness, marrow, meat, nub, pith, sum, nitty-
       gritty]

Moby Thesaurus II by Grady Ward, 1.0:

71 Moby Thesaurus words for "marrow":
   abatis, axiom, axis, bottom, brains, center, center of action,
   center of gravity, centroid, centrum, chitterlings, cockscomb,
   core, dead center, distillate, distillation, elixir, epicenter,
   essence, essential, essentiality, fabric, flower, focus,
   fundamental, giblets, gist, gizzard, gravamen, haslet, heart, hub,
   hypostasis, inner essence, kernel, kidneys, liver, material,
   matter, meat, medium, medulla, metacenter, middle, nave, navel,
   nub, nucleus, nuts and bolts, omphalos, pith, pivot, postulate,
   principle, quid, quiddity, quintessence, quintessential, sap, soul,
   spirit, storm center, stuff, substance, sum and substance,
   sweetbread, the nitty-gritty, tongue, tripe, umbilicus,
   virtuality