The Collaborative International Dictionary of English v.0.48:

Shadow \Shad"ow\, v. t. [imp. & p. p. Shadowed; p. pr. & vb.
   n. Shadowing.] [OE. shadowen, AS. sceadwian. See adow,
   n.]
   1. To cut off light from; to put in shade; to shade; to throw
      a shadow upon; to overspead with obscurity.
      [1913 Webster]

            The warlike elf much wondered at this tree,
            So fair and great, that shadowed all the ground.
                                                  --Spenser.
      [1913 Webster]

   2. To conceal; to hide; to screen. [R.]
      [1913 Webster]

            Let every soldier hew him down a bough.
            And bear't before him; thereby shall we shadow
            The numbers of our host.              --Shak.
      [1913 Webster]

   3. To protect; to shelter from danger; to shroud.
      [1913 Webster]

            Shadowing their right under your wings of war.
                                                  --Shak.
      [1913 Webster]

   4. To mark with gradations of light or color; to shade.
      [1913 Webster]

   5. To represent faintly or imperfectly; to adumbrate; hence,
      to represent typically.
      [1913 Webster]

            Augustus is shadowed in the person of [AE]neas.
                                                  --Dryden.
      [1913 Webster]

   6. To cloud; to darken; to cast a gloom over.
      [1913 Webster]

            The shadowed livery of the burnished sun. --Shak.
      [1913 Webster]

            Why sad?
            I must not see the face O love thus shadowed.
                                                  --Beau. & Fl.
      [1913 Webster]

   7. To attend as closely as a shadow; to follow and watch
      closely, especially in a secret or unobserved manner; as,
      a detective shadows a criminal.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Shadow \Shad"ow\ (sh[a^]d"[-o]), n. [Originally the same word as
   shade. [root]162. See Shade.]
   1. Shade within defined limits; obscurity or deprivation of
      light, apparent on a surface, and representing the form of
      the body which intercepts the rays of light; as, the
      shadow of a man, of a tree, or of a tower. See the Note
      under Shade, n., 1.
      [1913 Webster]

   2. Darkness; shade; obscurity.
      [1913 Webster]

            Night's sable shadows from the ocean rise. --Denham.
      [1913 Webster]

   3. A shaded place; shelter; protection; security.
      [1913 Webster]

            In secret shadow from the sunny ray,
            On a sweet bed of lilies softly laid. --Spenser.
      [1913 Webster]

   4. A reflected image, as in a mirror or in water. --Shak.
      [1913 Webster]

   5. That which follows or attends a person or thing like a
      shadow; an inseparable companion; hence, an obsequious
      follower.
      [1913 Webster]

            Sin and her shadow Death.             --Milton.
      [1913 Webster]

   6. A spirit; a ghost; a shade; a phantom. "Hence, horrible
      shadow!" --Shak.
      [1913 Webster]

   7. An imperfect and faint representation; adumbration;
      indistinct image; dim bodying forth; hence, mystical
      representation; type.
      [1913 Webster]

            The law having a shadow of good things to come.
                                                  --Heb. x. 1.
      [1913 Webster]

            [Types] and shadows of that destined seed. --Milton.
      [1913 Webster]

   8. A small degree; a shade. "No variableness, neither shadow
      of turning." --James i. 17.
      [1913 Webster]

   9. An uninvited guest coming with one who is invited. [A
      Latinism] --Nares.
      [1913 Webster]

            I must not have my board pastered with shadows
            That under other men's protection break in
            Without invitement.                   --Massinger.
      [1913 Webster]

   Shadow of death, darkness or gloom like that caused by the
      presence or the impending of death. --Ps. xxiii. 4.
      [1913 Webster]

WordNet (r) 3.0 (2006):

shadow
    n 1: shade within clear boundaries
    2: an unilluminated area; "he moved off into the darkness" [syn:
       darkness, dark, shadow]
    3: something existing in perception only; "a ghostly apparition
       at midnight" [syn: apparition, phantom, phantasm,
       phantasma, fantasm, shadow]
    4: a premonition of something adverse; "a shadow over his
       happiness"
    5: an indication that something has been present; "there wasn't
       a trace of evidence for the claim"; "a tincture of
       condescension" [syn: trace, vestige, tincture,
       shadow]
    6: refuge from danger or observation; "he felt secure in his
       father's shadow"
    7: a dominating and pervasive presence; "he received little
       recognition working in the shadow of his father"
    8: a spy employed to follow someone and report their movements
       [syn: tail, shadow, shadower]
    9: an inseparable companion; "the poor child was his mother's
       shadow"
    v 1: follow, usually without the person's knowledge; "The police
         are shadowing her"
    2: cast a shadow over [syn: shadow, shade, shade off]
    3: make appear small by comparison; "This year's debt dwarfs
       that of last year" [syn: shadow, overshadow, dwarf]

The Free On-line Dictionary of Computing (19 January 2023):

SHADOW

    A syntax-directed compiler written by Barnett
   and Futrelle in 1962.  It was the predecessor to SNOBOL(?)

   [Sammet 1969, p. 448, 605].

   (1995-01-16)