What do you call?

I have had someone challenge my definition of thief and liar?

So please clarify for me...

1. What do you call someone who borrows something, but does not return it?

And...

2. what do you call someone who does not tell the truth?

Please let me know. Because my answers are:

1. Thief

the definition of thief in the dictionary: One who steals.

2. Liar

The definition of liar in the dictionary: One that tells lies.