1. to (cause to) re-enter into an engagement to serve in the armed forces
They advised their men not to re-enlist when their time was up but to go home.
Half the soldiers were not planning to re-enlist.
The Army is now so overstretched it is prepared to re-enlist men who haven't fireda shot in anger since the Lee Enfield was a standard issue.
2. to re-enter into or re-engage in an enterprise, cause, etc
You don't get many offers to re-enlist in the National Football League.