Duty was a moral or legal obligation.
Although old and weary, the War Doctor fought the Last Great Time War due to duty. (AUDIO: The Innocent [+]Loading...["The Innocent (audio story)"])
Leef Apple Glyn Slitheen-Blathereen claimed that the Blathereen hunted the Slitheen for duty rather than profit. (TV: The Gift [+]Loading...["The Gift (TV story)"])
As a journalist, Cathy Salt felt that she had a duty to report facts. (TV: Boom Town [+]Loading...["Boom Town (TV story)"])
The Doctor claimed he had a duty of care, which extended to Clara Oswald (TV: Under the Lake [+]Loading...["Under the Lake (TV story)"], The Girl Who Died [+]Loading...["The Girl Who Died (TV story)"], Hell Bent [+]Loading...["Hell Bent (TV story)"]) and the Eleven, (AUDIO: Whisper [+]Loading...["Whisper (audio story)"]) which he took very seriously. (TV: Under the Lake [+]Loading...["Under the Lake (TV story)"])