Definition of tool noun from the Oxford Advanced American Dictionary
1 an instrument such as a hammer, screwdriver, saw, etc. that you hold in your hand and use for making things, repairing things, etc.garden toolsa cutting toolpower tools (= using electricity)Always select the right tool for the job.2 a thing that helps you to do your job or to achieve somethingresearch tools like questionnairesThe computer is now an invaluable tool for the family doctor.Some of them carried the guns which were the tools of their trade (= the things they needed to do their job).the effectiveness of interest rates as an economic tool3 a person who is used or controlled by another person or groupThe senator was an unwitting tool of the president. objects you can useIt is useful to know some general words to help you describe objects, especially if you do not know the name of a particular object.A device is something that has been designed to do a particular job: Have you seen the new device for cars that warns drivers about traffic jams ahead?A gadget is a small object that does something useful, but is not really necessary: His kitchen is full of gadgets he never uses.An instrument is used especially for delicate or scientific work: A thermometer is an instrument that measures temperature.A tool is something that you use for making and repairing things: A tool for turning screws is called a screwdriver.A machine has moving parts and is used for a particular job. It usually stands on its own: A blender is an electric machine for mixing soft food or liquid.An appliance is a large machine that you use in the house, such as a washing machine.Equipment means all the things you need for a particular activity: rock climbing equipment.Apparatus means all the tools, machines, or equipment that you need for something: firefighters wearing breathing apparatus.