enter

enter /ˈɛntɚ/ verb
enters; entered; entering
enter
/ˈɛntɚ/
verb
enters; entered; entering
Britannica Dictionary definition of ENTER
1 
: to go or come into (something)
[+ object]
[no object]
— opposite exit
2 
[+ object]
a  : to begin to be in (an organization, school, etc.)
b  : to cause (someone) to be in an organization, school, etc.
3 
[+ object]
a  : to start to do something
b  : to begin to be in (a particular situation, period of time, etc.)
c  : to appear for the first time in (something)
4 
a  : to officially say that you will be in a race, competition, etc.
[+ object]
[no object]
b  [+ object] : to officially say that (someone) will be in a race, competition, etc.
◊ If you are entered in a race, competition, etc., you are one of the people who are competing in it.
5 
[+ object]
a  : to include (something) in a book, list, etc.
b  : to type in (words, data, etc.) on a computer
6 
[+ object] : to make or state (something) in a formal and official way

enter into

[phrasal verb]
1 
enter into (something)
: to begin to be in or to take part in (something)
2 
: to be a part of or to influence (something, such as a choice or decision)
3 
: to share or become involved in (something)

enter on/upon

[phrasal verb]
enter on/upon (something)
: to begin to be in or to take part in (something)

enter the picture/scene

1 
: to become involved in something
2 
or enter (into) the equation : to become something that must be considered or dealt with

enter your mind/head

: to occur in your thoughts