The phrase "tie into" generally means to connect or link with something. There are various synonyms available for this phrase which can be used in different contexts. Some of the synonyms for "tie into" include associate with, relate to, attach to, connect with, link with, bind with, refer to, engage with, and have to do with. All these phrases suggest that there is a close relationship between two things. For instance, you can tie into a project, meaning that you are fully committed to it and it is an essential part of your work. Alternatively, you can tie into a particular conversation, meaning that you are closely related and can understand the topic at hand.