lag¹ / lag/ • v. (lagged, lag·ging) [intr.] fall behind in movement, progress, or development; not keep pace with another or others: they stopped to wait for one of the children who was lagging behind.• n. 1. (also time lag) a period of time between one event or phenomenon and another: there was a time lag between the commission of the crime and its reporting to the police.2. Physics a retardation in an electric current or movement.DERIVATIVES: lag·ger n.lag² • v. (lagged, lag·ging) [tr.] (usu. be lagged) enclose or cover (a boiler, pipes, etc.) with material that provides heat insulation: [as adj.] (lagged) a lagged hot-water tank. • n. the nonheat-conducting cover of a boiler, etc.; lagging. ∎  a piece of this.DERIVATIVES: lag·ger n.lag³ chiefly Brit., inf. • n. a person who has been frequently convicted and sent to prison: both old lags were sentenced to ten years' imprisonment.• v. (lagged , lag·ging ) [tr.] archaic arrest or send to prison.

lag A normal, dip-slip fault, dipping less than 45°, on which there has been a relative downward displacement of the hanging wall. See also FAULT.

lag1 fail to keep pace, fall behind. XVI. contemp. with lag sb.1 last or hindmost person, and adj. hindmost, falling behind, which may be a perversion of LAST3 in fog, seg, lag, used dial. in children's games for ‘first, second, last’.

lag3 stave of a barrel XVII; lath or strip of material in a covering or casing (whence vb.) XIX. prob. of Scand. orig., cf. ON. lǫgg rim of a barrel, f. Gmc. *laʒ-LAY1.

lag2 †carry off, steal XVI; (sl.) transport, apprehend XIX. of unkn. orig.
Hence lag sb.2 (sl.) convict; term of penal servitude. XIX.