Noah Webster
Lag
LAG, adjective [This word belongs to the root of slack, slow, sluggish, languish, long; Gr. See the Verb.]
1. Coming after or behind; slow; sluggish; tardy.
2. Last; long delayed; as the lag end.
[This adjective is not now in use.]
LAG, noun
1. The lowest class; the rump; the fag end.
2. He that comes behind. [Not in use.]
LAG, verb intransitive [Eng. to flag, and flacceo, langueo, to languish, etc. The sense is to extend or draw out, or to become lax or loose.]
To walk or move slowly; to loiter; to stay behind.
I shall not lag behind.