The only idiot in the village...

[Llosgi Calch]

Whilst the answer to this question could be answered in my local village by someone with a trained eye...(or even by viewing the members of this site)

Can someone please fully distinguish the difference between...

[a] an idiot
a lunatic
[c] an imbecile

Whilst these are today traded as insults, on the census of the 19th century they appear to be description's of seperate actual medical disabilities/conditions

['Tricia]

imbecile: as an adjective meaning (mainly physically) weak, or impotent. Via French from the Latin for "without support". It acquired its meaning of mentally weak in the early nineteenth century. Became a legal definition in 1913

lunatic
In its original Latin it was a type of periodic insanity believed to be affected by the phases of the moon (luna), but it entered English law as the term for such an unsoundness of mind as justified interfering with a person's civil rights, or considering their transactions invalid.

idiot
via French from the Latin for an ignorant person, it meant in English a person of extremely low intelligence 

Clear as mud!