Enter somewhere or something; also fit inside something. For example, Don't go into this building, or The tractor is too big to go into the shed. [c. a.d. 1000]
Enter a particular state or condition, as in She's about to go into hysterics, or I'm afraid he went into a coma. [Second half of 1600s]
Investigate or discuss, especially in detail. For example, We haven't time to go into the entire history of the project. [Early 1800s] Also see enter into, def. 4. Also see the subsequent entries beginning with go into.