Source : Webster's Revised Unabridged Dictionary (1913)

Lagging \Lag"ging\, n.
   1. (Mach.) The clothing (esp., an outer, wooden covering), as
      of a steam cylinder, applied to prevent the radiation of
      heat; a covering of lags; -- called also {deading} and
      {cleading}.

   2. Lags, collectively; narrow planks extending from one rib
      to another in the centering of arches.