(Lat. ingenium), a term which in the time of Chaucer had the meaning of "natural talent" or "ability," corresponding to the Latin from which it is derived (cf. "A man bath sapiences thre, Memorie, engin, and intellect also," Second Nun's Tale, 339); in this sense it is now obsolete. It also denoted a mechanical tool or contrivance, and especially a weapon of war; this use may be compared with that of ingenium in classical Latin to mean a clever idea or device, and in later Latin, as in Tertullian, for a warlike instrument or machine. In the 19th century it came to have, when employed alone, a specific reference to the steam-engine, but it is also used of other prime movers such as the air-engine, gas-engine and oil-engine (qq.v.).