The Collaborative International Dictionary of English v.0.48:

Sliding \Slid"ing\, a.
   1. That slides or slips; gliding; moving smoothly.
      [1913 Webster]

   2. Slippery; elusory. [Obs.]
      [1913 Webster]

            That sliding science hath me made so bare.
                                                  --Chaucer.
      [1913 Webster]

   Sliding friction (Mech.), the resistance one body meets
      with in sliding along the surface of another, as
      distinguished from rolling friction.

   Sliding gunter (Naut.), a topmast arranged with metallic
      fittings so as to be hoisted and lowered by means of
      halyards.

   Sliding keel (Naut), a movable keel, similar to a
      centeboard.

   Sliding pair. (Mech.) See the Note under Pair, n., 7.

   Sliding rule. Same as Slide rule, under Slide, n.

   Sliding scale.
      (a) A scale for raising or lowering imposts in proportion
          to the fall or rise of prices.
      (b) A variable scale of wages or of prices.
      (c) A slide rule.

   Sliding ways (Naut.), the timber guides used in launching a
      vessel.
      [1913 Webster]

WordNet (r) 3.0 (2006):

sliding
    adj 1: being a smooth continuous motion

Moby Thesaurus II by Grady Ward, 1.0:

52 Moby Thesaurus words for "sliding":
   coasting, coming apart, cracking, crumbling, decadent, declining,
   degenerate, deteriorating, disintegrating, draining, drooping,
   dwindling, ebbing, effete, fading, failing, falling, flagging,
   flow, flowing, fragmenting, glide, gliding, going to pieces,
   languishing, marcescent, pining, regressive, retrograde,
   retrogressive, sailing, shriveling, sinking, skating, skiing, skim,
   sledding, slide, slipping, slither, slithering, slumping,
   subsiding, sweep, sweeping, tabetic, tobogganing, waning, wasting,
   wilting, withering, worsening