The most common and most likely answer to this crossword clue is the 6 letter word PHYSIC
I've seen this crossword clue in The Guardian
P
H
Y
S
I
C
More clues leading to the result PHYSIC
- Past caring?
- Something healing scientist drops first
- Old medicinal lesson cut short
- In radiography sickness has a cure
- Medicine is singular subject
- Archaic treatment of shy bats captured in photo
- Film about shy doctor of medicine
- Sophy sick? Out-of-date medicine has contributed to that
- In radiography, sickness is given a cure
- Medicinal science is curtailed
Buddy explains!

The straight part
We know that "Archaic treatment" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case archaic treatment = physic.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does PHYSIC mean?
PHYSIC noun- A medicine or drug, especially a cathartic or purgative.
- The art or profession of healing disease; medicine.
- Natural philosophy; physics.
- A physician.
- To cure or heal.
- To administer medicine to, especially a purgative.
- Relating to or concerning existent materials; physical.