Go or come in again (7)
(Other definitions for re-enter that I've seen before include "Come back inside" , "Go back in" , "Come or go in again" , "compete again" .)
(Other definitions for reenter that I've seen before include "Go/come in again" , "Terrene (anag.)" , "Go in again" , "Penetrate again" , "Come back inside" .)