2
general::
1. Enter, especially into a building. For example, It's cold out here, so can we go in? [Tenth century A. D.] 2. Be obscured, as in After the sun went in, it got quite chilly. [Late 1800s] 3. go in with. Join others in some venture. For example, He went in with the others to buy her a present. [Late 1800s] Also see the subsequent idioms beginning with GO IN.
American Heritage Idioms