One history of medicine book credits Giovanni Filippo (1510–1580) of Palermo with the first description of varicella (chickenpox). Subsequently in the 1600s, an English physician named Richard Morton described what he thought a mild form of smallpox as “chicken pox.” Later, in 1767, a physician named William Heberden, also from England, was the first physician to clearly demonstrate that chickenpox was different from smallpox. However, it is believed the name chickenpox was commonly used in earlier centuries before doctors identified the disease.

I hope this helps.

There are many explanations offered for the origin of the name chickenpox:

Samuel Johnson suggested that the disease was “no very great danger”, thus a “chicken” version of the pox;

the specks that appear looked as though the skin was pecked by chickens;

the disease was named after chick peas, from a supposed similarity in size of the seed to the lesions;

the term reflects a corruption of the Old English word giccin, which meant itching.

As “pox” also means curse, in medieval times some believed it was a plague brought on to curse children by the use of black magic.

From ancient times, neem has been used by Indians to alleviate the external symptoms of itching and to minimise scarring. Neem baths (neem leaves and a dash of turmeric powder in water) are commonly given for the duration.

During the medieval era, oatmeal was discovered to soothe the sores, and oatmeal baths are today still commonly given to relieve itching.