Private is a synonym for

personal

thoughtful

public

simple

Personal because your privacy is personal

personal

Explanation:

Here is the definition for Private on the internet:

belonging to or for the use of one particular person or group of people only.

In that case, we can rule out Public, Simple, and Thoughtful. By process of elimination, we have only one option left--personal. Thus, our answer is personal.

Also, to add to that, the definition states, " ... of one particular person or group ... "

Since person is the base word and - al is our suffix, personal is our final answer.