n (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.
n A tool in mountaineering that is driven into the snow and used as an anchor or to arrest falls.
n (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.
n A sentry. Can be used figuratively.
n A protester positioned outside an office, workplace etc. during a strike (usually in plural); also the protest itself.
v (intransitive) To protest, organized by a labour union, typically in front of the location of employment.
v (transitive) To enclose or fortify with pickets or pointed stakes.
v (transitive) To tether to, or as if to, a picket.
v (transitive) To guard, as a camp or road, by an outlying picket.
v (obsolete|transitive) To torture by forcing to stand with one foot on a pointed stake.