Picket

From French piquet, from piquer ("to pierce").

Full definition of picket

(plural pickets)

A stake driven into the ground.
a picket fence
(historical) A type of punishment by which an offender had to rest his or her entire body weight on the top of a small stake.
A tool in mountaineering that is driven into the snow and used as an anchor or to arrest falls.
(military) Soldiers or troops placed on a line forward of a position to warn against an enemy advance. It can also refer to any unit (for example, an aircraft or ship) performing a similar function.

1990, Peter Hopkirk, The Great Game, Folio Society 2010, p. 59:So confident was he that he ignored the warning of his two British advisers to post pickets to watch the river, and even withdrew those they had placed there.

1907, w, The Dust of Conflict Chapter 26, Maccario, it was evident, did not care to take the risk of blundering upon a picket, and a man led them by twisting paths until at last the hacienda rose blackly before them.

A protester positioned outside an office, workplace etc. during a strike (usually in plural); also the protest itself.
Pickets normally endeavor to be non-violent.

1918, W. B. Maxwell, The Mirror and the Lamp Chapter 22, In the autumn there was a row at some cement works about the unskilled labour men. A union had just been started for them and all but a few joined. One of these blacklegs was laid for by a picket and knocked out of time.

(intransitive) To protest, organized by a labour union, typically in front of the location of employment.
(transitive) To enclose or fortify with pickets or pointed stakes.
(transitive) To tether to, or as if to, a picket.to picket a horse
(transitive) To guard, as a camp or road, by an outlying picket.
(obsolete, transitive) To torture by forcing to stand with one foot on a pointed stake.