Definitions of lag:

• noun:   the act of slowing down or falling behind
• noun:   one of several thin slats of wood forming the sides of a barrel or bucket
• noun:   the time between one event, process, or period and another
• verb:   cover with lagging to prevent heat loss

  Example: "Lag pipes"

• verb:   throw or pitch at a mark, as with coins
• verb:   hang (back) or fall (behind) in movement, progress, development, etc.
• verb:   lock up or confine, in or as in a jail