Physic comes from the Latin word for "study of nature," so it's unclear how it came to mean a "purging medicine." An almost-synonym is "cathartic," although that word is usually used to describe an emotional purging- like a good cry- rather than physical one.

Where does the word physic come from?

The word "physics" comes from Ancient Greek: φυσική (ἐπιστήμη), romanized: physikḗ (epistḗmē), meaning "knowledge of nature".

Is physics a Greek word?

Physics is a branch of science. ... The word physics comes from the Greek word ἡ φύσις, meaning "nature". Physics can also be defined as "that department of knowledge which relates to the order of nature, or, in other words, to the regular succession of events".