The Collaborative International Dictionary of English v.0.48:

Lag \Lag\, v. i. [imp. & p. p. Lagged; p. pr. & vb. n.
   Lagging.]
   To walk or more slowly; to stay or fall behind; to linger or
   loiter. "I shall not lag behind." --Milton.

   Syn: To loiter; linger; saunter; delay; be tardy.
        [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

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]

WordNet (r) 3.0 (2006):

lagging
    n 1: used to wrap around pipes or boilers or laid in attics to
         prevent loss of heat

Moby Thesaurus II by Grady Ward, 1.0:

70 Moby Thesaurus words for "lagging":
   Micawberish, afterthought, backward, bind, block, blockage,
   bureaucratic delay, dalliance, dallying, dawdling, delay, delayage,
   delayed reaction, delaying, detention, dilatoriness, dilatory,
   dillydallying, double take, dragging, easygoing, foot-dragging,
   halt, hang-up, hindrance, holdup, interim, jam, lackadaisical, lag,
   laggard, lax, lazy, lingering, logjam, loitering, lollygagging,
   moratorium, obstruction, paperasserie, pause, procrastinating,
   procrastination, procrastinative, procrastinatory, red tape,
   red-tapeism, red-tapery, remiss, reprieve, respite, retardance,
   retardation, shilly-shallying, shuffling, slack, slow, slow-up,
   slowdown, slowness, sluggish, stay, stay of execution, stop,
   stoppage, suspension, tarrying, tie-up, time lag, wait