Why is doulos translated slave sometimes and bond servant others?

Romans 1:1 in the NASB is translated Paul, a bond servant. "bond-servant" is a translation of the Greek word "doulos" Strongs 1401. Why is it translated slave usually, but in other places (like Ro 1:1) it is translated bond-servant?

Romans 1:1

NASB - ¹ Paul, a bond-servant of Christ Jesus, called as an apostle, set apart for the gospel of God.

Clarify • Share • Report • Asked November 03 2013 • Mike walker Supporter