【Device】 , 【contrivance】 , 【gadget】 , 【contraption】 mean something usually of a mechanical character which is invented as a means of doing a particular piece of work or of effecting a given end.

【Device】 is the most widely applicable of these terms; it may be used of a thing that serves as a tool or instrument or as an effective part of a machine, especially one which shows some ingenuity in invention.

It may be used also of an artifice or stratagem concocted as a means of accomplishing an end or of a pattern or design that shows the play of fancy, especially of one that proves useful to the less inventive.

【Contrivance】 stresses skill and dexterity in the adaptation of means and especially of the means at hand to an end; it sometimes carries a suggestion of crudity of or of contempt for the resulting  【device】 or system.

【Gadget】 is sometimes used of a 【device】 for which one does not know the name; more often it applies to a small and novel 【device】 and especially to an accessory or an appliance intended to add to a person’s comfort, convenience, or pleasure.

【Contraption】 is usually more depreciative than 【contrivance】 or 【gadget】 and often suggests a clumsy substitute rather than an ingenious invention.

It also may denote something viewed with skepticism or mistrust primarily because new, unfamiliar, or untried.