ˈäd.(ˌ)ō, ˈä(ˌ)tō- noun
Usage: usually capitalized O
Etymology: after Nikolaus A. Otto died 1891 German technician and inventor
: a four-stroke cycle for internal-combustion engines of the type used in automobiles wherein the first stroke consists of the suction into the cylinder of the explosive charge (as gas and air), the second stroke consists of the compression, ignition, and explosion of the charge, the third stroke consists of the expansion of the gases, and the fourth stroke consists of the expulsion of the products of combustion from the cylinder