"Troop" may also be an intransitive verb meaning "to move or go as a throng."
The word "troop" dates to the mid-1500's, when the English military appropriated the Middle French word "troupe" for a group of soldiers.
"Troupe" comes from the Old French word "trope," derived from tropeau, which means "flock" or "herd." Scholars believe that "tropeau" came from the Latin "troppus," which came from the same ancient German sources that gave us "thorp" and "throp," the Middle English terms for "hamlet" or "village."
The English word "troupe" was re-borrowed from the French in about 1825, this time retaining its French spelling and used solely to refer to a group of theatrical performers.
"Troop" should not be used to refer to a single person, but it may be used for as few as two troops. There must be at least five Boy Scouts or Girl Scouts in a troop, and there are usually about 60 troopers in a calvary troop.
"Trooper" means a state police officer or a soldier, while "trouper" means a member of a performing company.
"Trouper" also means someone who is a hard worker or endures hardships, as in "What a trouper." This usage dates to at least 1959, when it was already considered old-fashioned.