pick·et 
(pĭkĭt)
(pĭkĭt)n.
1. A pointed stake often driven into the ground to support a fence, secure a tent, tether animals, mark points in surveying, or, when pointed at the top, serve as a defense.
2. A detachment of one or more troops, ships, or aircraft held in readiness or advanced to warn of an enemy's approach: "The outlying sonar picket ... was to detect, localize, and engage any submarine trying to close the convoy" (Tom Clancy).
3.
a. A person or group of persons stationed outside a place of employment, usually during a strike, to express grievance or protest and discourage entry by nonstriking employees or customers.
b. A person or group of persons present outside a building to protest.
v. pick·et·ed, pick·et·ing, pick·ets
v.tr.
1. To enclose, secure, tether, mark out, or fortify with pickets.
2.
a. To post as a picket.
b. To guard with a picket.
3. To post a picket or pickets during a strike or demonstration.
v.intr.
To act or serve as a picket.
[French piquet, from Old French, from piquer, to prick; see PIQUE.]
picket·er n.