any device, contraption or machinery, particularly a complex, dangerous or powerful one; a piece of military equipment; a piece of heavy machinery; any object whose name or function is unknown; a thingy; a gizmo; tool (penis)
“Ça a pas été trop dur, parce que je suis une bonne reproductrice, je suis quand même tombée enceinte alors que j'avais un stérilet, et j'ai des jumeaux (mes petits frère et sœur), alors bon, et, ça reste entre nous, mais ton père il a un sacre engin.” — It wasn't too hard, because I'm very fertile; I still got pregnant even though I had an IUD, and I have twins (my little brother and sister). You see, and this is just between you and me, but your father has a hell of a tool on him.
Inherited from Middle French engin m, from Old French engin m, from Latin ingenium n.