counterpoise (n.)

early 15c., "a weight equal to and balancing another; any equal power or force acting in opposition," from Old French contrepois (Modern French contrepoids), from contre- "against" (see contra-) + peis, from Latin pensum "weight," noun use of neuter past participle of pendere "to hang, cause to hang; weigh" (from PIE root *(s)pen- "to draw, stretch, spin").

As a verb, "to act in opposition to," late 14c. (implied in counterpoised), from Old French contrepeser.