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]