v. set, setÂ·ting, sets. v.tr. 1. To put in a specified position or arrangement; place: set a book on a table; set the photo next to the flowers. 2. a. To put into a specified state: set the prisoner at liberty; set the house ablaze; set the machine in motion. b. To cause to begin an action: The noise set the dog to barking. c. To cause or assign (someone) to undertake an action or perform a service: The sergeant set the recruit to sweeping the barracks.