Tear

Tears, or lachrymatory secretions, were the liquids secreted from an individuals' eyes during the act of crying. This could be caused by stress or pain, (COMIC: The Infinite Astronaut) as well as grief, guilt, anger and panic. (AUDIO: Harvest of the Sycorax)

The automatic visor washers Carl Readon installed in the robot, Robbie allowed him to produce tears. (COMIC: Doctor Who and the Robot)

After Heather became a sentient oil creature, she "left her tears" with Bill Potts. (TV: The Pilot) After being cyberconverted, Bill cried, (TV: World Enough and Time) with the Twelfth Doctor later assuring her "where there's tears there's hope". Heather traced Bill by the tears Heather left her, and made her another sentient oil creature. Bill, in turn, saved the Doctor with her tears. (TV: The Doctor Falls)