παρεισέρχομαι/pareiserchomai

This word is an action. It is a verb.

This word can mean to enter a group pretending to be part of it but really intending to harm it.
This word can mean to come in closely beside something. This word is used to talk about something becoming a part of a situation in such a way as to change the situation.

See: Galatians 2:4; Romans 5:20