Definition of SET UP. 1. a: to raise to and place in a high position b: to place in view: post c: to put forward (as a plan) for acceptance. 2.b: to assemble the parts of and erect in position c: to put (a machine) in readiness or adjustment for an operation.3. b: bring about.4.efinition of SET UP. 1. a: to raise to and place in a high position b: to place in view: post c: to put forward (as a plan) for acceptance. 2.