Soldiers posted on guard ahead of a main force. Pickets included about 40 or 50 men each. Several pickets would form a rough line in front of the main army's camp. In case of enemy attack, the pickets usually would have time to warn the rest of the force.

A person, or persons, posted at the entrance of a place of work which is affected by a strike, in order to stop people entering the premises.

1745, "to enclose with pickets," from picket (n.). The sense in labor strikes, protests, etc., is attested from 1867. Related: Picketed; picketing.

1680s, "pointed stake (for defense against cavalry, etc.)," from French piquet "pointed stake," from piquer "to pierce" (see pike (n.2)). Sense of "troops posted to [..]

serve as pickets or post pickets; "picket a business to protest the layoffs" lookout: a person employed to keep watch for some anticipated event a detachment of troops guardi [..]

(or picquet) guard-outpost or stake for tying horses

A small party of foot soldiers sent in advance of the army to feel out the enemy and harass him if he approaches. Highly likely to be composed of Light infantry. Pickets:

a person posted by a labor organization at a place of employment affected by a labor dispute ;broadly : a person posted for a demonstration or protest

(n) a person employed to keep watch for some anticipated event(n) a detachment of troops guarding an army from surprise attack(n) a protester posted by a labor organization outside a place of work(n)  [..]