Track DownTo track down means to seek and find where something or someone is.
Ex: Have you seen Mary recently? I'm trying to track her down because one of her clients left an important message for her.
Ex: Carl was having a hard time researching the topic of his paper, but the reference librarian helped him by tracking down a few good academic sources.
To cover your tracks means to hide what you were doing or to destroy evidence of what you were doing.
Ex: Vincent wanted to make sure that his wife's birthday party was a surprise, so he was careful to cover his tracks so that she wouldn't become suspicious.
Ex: The murderer thought he'd covered his tracks by hiding the murder weapon, but the police were able to find his hiding place easily.
RelationshipThe state of being connected or the way in which two concepts, objects or people are connected is their relationship.
Ex: Wendy asked what Jim and my relationship is and I explained that he's my cousinin-law because he's married to my cousin Sherry.
Ex: The relationship between cancer and smoking is well known, and it's a causal one. Smoking tobacco simply causes lung cancer, and a lot of other lung problems, too.
Any two people who are connected have a relationship but when we say two people are in a relationship, it means they are dating each other romantically. When the relationship ends, they break up.
Ex: Erin and Scott started going out last year. They're in a pretty serious relationship now, actually. I think they might start talking about marriage.
Ex: I don't think we should invite Dave to the party. He and Chris have actually broken up recently and I don't want to create any awkward situations for them.