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.
      1913 webster

   2. lags, collectively; narrow planks extending from one rib
      to another in the centering of arches.
      1913 webster
see also:
deading cleading