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.
2. The fag-end; the rump; hence, the lowest class.
The common lag of people. --Shak.
3. The amount of retardation of anything, as of a valve in a
steam engine, in opening or closing.
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.
5. (Zool.) See Graylag.
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
[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.