These words are often found in medical books from the 19th century and earlier, medical records and death certificates. Definitions for some terms do not have current equivilents because the term was used as a catchall when a more specific diagnosis wasn't possible such as apoplexy or the disease was in fact a symptom such as fever. Terms such as syphilis with serious social stigma attached to them were often avoided on death certificates and general terms such as fever, heart disease, dementia or paralysis written in their place.
The Oxford English Dictionary is, of course, the mother of all English dictionaries and the preeminent source for definitions, etymologies and usage over time from Anglo Saxon to contemporary English all over the world.
If the OED contains the word, "OED" and the date of its first reported publication is included. If there is a 'c' in front of the date, it stands for 'circa' which means that the date is approximate. Otherwise another source, location of usage and broad time frame such as "19th cent." is provided where possible.