The Collaborative International Dictionary of English v.0.48:

Lag \Lag\, n.
   1. One who lags; that which comes in last. [Obs.] "The lag of
      all the flock." --Pope.
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   2. The fag-end; the rump; hence, the lowest class.
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            The common lag of people.             --Shak.
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   3. The amount of retardation of anything, as of a valve in a
      steam engine, in opening or closing.
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   4. A stave of a cask, drum, etc.; especially: (Mach.), one of
      the narrow boards or staves forming the covering of a
      cylindrical object, as a boiler, or the cylinder of a
      carding machine or a steam engine.
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   5. (Zool.) See Graylag.
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   6. The failing behind or retardation of one phenomenon with
      respect to another to which it is closely related; as, the
      lag of magnetization compared with the magnetizing force
      (hysteresis); the lag of the current in an alternating
      circuit behind the impressed electro-motive force which
      produced it.
      [Webster 1913 Suppl.]

   Lag of the tide, the interval by which the time of high
      water falls behind the mean time, in the first and third
      quarters of the moon; -- opposed to priming of the tide,
      or the acceleration of the time of high water, in the
      second and fourth quarters; depending on the relative
      positions of the sun and moon.

   Lag screw, an iron bolt with a square head, a sharp-edged
      thread, and a sharp point, adapted for screwing into wood;
      a screw for fastening lags.
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