c.1300, "mechanical device," especially one used in war; "manner of construction," also "skill, craft, innate ability; deceitfulness, trickery," from Old French engin "skill, wit, cleverness," also "trick, deceit, stratagem; war machine" (12c.), from Latin ingenium "inborn qualities, talent" (see ingenious), in Late Latin "a war engine, battering ram" (Tertullian, Isidore of Seville). Sense of "device that converts energy to mechanical power" is 18c.; in 19c. especially of steam engines.