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.
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   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:

Shadowing \Shad"ow*ing\, n.
   1. Shade, or gradation of light and color; shading.
      --Feltham.
      [1913 Webster]

   2. A faint representation; an adumbration.
      [1913 Webster]

            There are . . . in savage theology shadowings,
            quaint or majestic, of the conception of a Supreme
            Deity.                                --Tylor.
      [1913 Webster]

WordNet (r) 3.0 (2006):

shadowing
    n 1: the act of following someone secretly [syn: shadowing,
         tailing]

Moby Thesaurus II by Grady Ward, 1.0:

71 Moby Thesaurus words for "shadowing":
   ambuscade, ambush, ambushment, blackening, blind,
   blocking the light, booby trap, bugging, chase, chasing,
   cloak-and-dagger work, clouding, counterespionage,
   counterintelligence, darkening, dimming, dogging, eclipsing,
   electronic surveillance, espial, espionage, extinguishment, follow,
   follow-up, following, heeling, hounding, hue and cry, hunting,
   intelligence, intelligence work, lurking hole,
   military intelligence, obfuscation, obnubilation, obscuration,
   obscurement, observation, obumbration, occulting, overcast,
   overclouding, overshading, overshadowing, overshadowment,
   prosecution, pursual, pursuance, pursuing, pursuit, quest,
   searching, secret police, secret service, seeking, sequel,
   sequence, series, shading, spying, stakeout, stalking,
   stalking-horse, surveillance, tailing, tracking, tracking down,
   trailing, trap, wiretap, wiretapping



The Free On-line Dictionary of Computing (30 December 2018):

aliasing
shadowing

   1.  When several different identifiers refer to the
   same object.  The term is very general and is used in many
   contexts.

   See alias, aliasing bug, anti-aliasing.

   2.  (Or "shadowing") Where a hardware device
   responds at multiple addresses because it only decodes a
   subset of the address lines, so different values on the
   other lines are ignored.

   (1998-03-13)