I apologize if this isn't the right sub for this. It's not a crosspost but it's similar to what I just posted in genetics, and I may not have the exact term right, but I'm pretty sure eccentricity is the right one. My folks always said it's an old catch-all medical term for someone who is robust and successful in life while clearly having a few screws loose, but not enough issues to force hospitalization.
My grandmother and her father had it, my grandmother's sister had something similar but not quite the same thing, and the reason this is relevant is because I got a milder version of it when I was a teenager, and two of my cousins now have the full blown version that my grandmother had. It's kind of like an unspecified learning disability. Doctors can't figure out what it is and are asking for a family medical history, but 'eccentricity' doesn't really tell them much.
I suppose it's worth pointing out that all of these people were very social and very brilliant. Definitely not the sort of people they'd be putting in a mental institution.
Nurse here (not a historian, I hope it is okay to post, let me know if I need to expand on something)... I can't speak to your situation specifically, but as no one has answered yet thought I would throw in my $0.02 (until you have a more comprehensive historically rooted answer)...
Generally 'eccentricity' was a catchall for a number of personality disorders and mental health diagnoses which became the "Cluster A" personality disorders in the DSM-5. They are still referred to a the "odd or eccentric personality disorders"...
Indicators of which include little to no self-awareness or understanding of consequence, irrational behavior and irrational justification for behavior, paranoia, strong need for independence (and avoidance of close relationships). If you want to look it up, look for Cluster A personality disorders (PD) and/or Paranoid PD, Schizoid PD, and Schizotypal PD would be the modern diagnoses.
It is important to note that prior to WWII there really was not much understanding of personality disorders, generally people who were diagnosed with 'eccentricity' were high functioning but 'odd', and notably unresponsive to medical treatment. (This can be seen as a contrast to disorders like Schizophrenia, or other mental health pathologies which are low functioning and for which medical treatment is effective today). In and before the 1940's mental health diagnoses and treatment was not really empirical, holistic or often scientific in comparison to what we know about the mind today, (or compared to pathologies of the body at that time).
WWII sparked a lot of the changes in understanding of mental health, the DSM was created in the late 1950's as a result, and treatment moved slowly from institutionalized care to clinical care... It still took many decades to developed the understanding we have today, but WWII was the turning point.
references:
Diagnostic and Statistical Manual of Mental Disorders (DSM), Fifth Edition (2013)
A History of Mental Health Nursing, (2013)