First Mention: LIAB Epilogue 11
Some Healomancers gain the title of Doctor. Pierce used this fact to encourage a captured Lilith not to be shy about needing to use the latrine in front of him. Presumably because he's "seen it all" and will treat her professionally rather than oggling her.
The title of doctor seems particular to healomancers, and possibly prone to being falsely claimed. Digdoug thought that "Doctor" Herbert Sassafras wasn't really one. Similarly, the Tonic of Wildness, a very cheap and low quality liquor, was made by a "doctor" Henry David Skidreau.
Doctors are Master-class Healomancers.
There is a "bar" or other peer association of Healomancers that reviews who can gain the title. Alternately, being a doctor is unrelated to level, it is earned some other way, such as battlefield experience or training in Erfworlder anatomy.