An entrance is something you go through and an exit is something you leave through :)
The word opposite of entrance is Exit
Entrance
Entrance to Exit - 1966 was released on: USA: 1966
Entrance
Opposites of entrance are exit, departure, egress, bore.
The opposite of the word entrance would be the word exit.
Entrance or exit
entrance
A portal is a hole. A portal exit is where you exit out of the hole. A portal entrance is where you enter into the hole.
Exit.
This is not an exact analogy, although entrance can be considered the opposite of exit. The "opposite" of minute (small) would be large, big, or huge.
The circular ring of muscle located at the entrance and exit of the stomach is referred to as a "sphincter" - the one at the entrance to the stomach is referred to as the cardiac sphincter, and the one at the exit of the stomach to the small intestines is referred to as the pyloric sphincter.