What does "sliding" mean?

Sliding: Slippery; elusory. [Obs.] That sliding science hath me made so bare. Chaucer. 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.