In third chapter of Little Dorrit, a man on Sunday remembers being compelled to go to chapel by a "piquet"
of teachers. That spelling in US dictionary is "picket"
for which third defintion of second word is:
3. [Probably so called from the picketing of the horses.]
(Mil.) A detached body of troops serving to guard an army
from surprise, and to oppose reconnoitering parties of the
enemy; -- called also outlying picket.