The most common and most likely answer to this crossword clue is the 5 letter word SANER
I've seen this crossword clue in Independent
S
A
N
E
R
Buddy explains!
The straight part
We know that "comparatively rational" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case comparatively rational = saner.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 SANER mean?
SANER adjective- Being in a healthy condition; not deranged; thinking rationally.
- Mentally sound; possessing a rational mind; having the mental faculties in such condition as to be able to anticipate and judge the effect of one's actions in an ordinary manner.
- Rational; reasonable; sensible.