The most common and most likely answer to this crossword clue is the 5 letter word FERMI
F
E
R
M
I
More clues leading to the result FERMI
- After a review, I declare myself the official physicist
- Self-identification of judge standing up – or physicist
- A grim reference turned up revealing the name of famous physicist
- Some prefer Michael to Enrico, perhaps
- Scientist part of safer mission
- Man of science rose and declared himself the arbiter
- Curiously fire male physicist
Buddy explains!

The straight part
We know that "Man of science" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case man of science = fermi.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 FERMI mean?
FERMI noun- An obsolete unit of length equal to one femtometer or femtometre (10−15 m).