a post, stake, pale, or peg that is used in a fence or barrier, to fasten down a tent, etc.

a person stationed by a union or the like outside a factory, store, mine, etc., in order to dissuade or prevent workers or customers from entering it during a strike.

a person engaged in any similar demonstration, as against a government's policies or actions, before an embassy, office building, construction project, etc.

Military . a soldier or detachment of soldiers placed on a line forward of a position to warn against an enemy advance.

Navy, Air Force . an aircraft or ship performing similar sentinel duty.

to enclose within a picket fence or stockade, as for protection, imprisonment, etc.

to picket a lawn; to picket captives.

to fasten or tether to a picket.

to place pickets in front of or around (a factory, store, mine, embassy, etc.), as during a strike or demonstration.

Military .

to guard, as with pickets.

to post as a picket.

to stand or march as a picket.