WordNet sense 1 (an elaborate or deceitful scheme contrived to deceive or evade):

dodge, stratagem

WordNet sense 2 (any improvised arrangement for temporary use):

lash-up

WordNet sense 3 (a device or control that is very useful for a particular job):

appliance, contraption, convenience, gadget, gismo, gizmo, widget

WordNet sense 4 (the act of devising something):

devisal