n. & v.
n. 1 a froth produced by agitating soap etc. and water. 2 frothy sweat, esp. of a horse. 3 a state of agitation.
v. 1 intr. (of soap etc.) form a lather. 2 tr. cover with lather. 3 intr. (of a horse etc.) develop or become covered with lather. 4 tr. colloq. thrash. lathery adj.
[ OE leathor (n.), lethran (v.) ]