The most common and most likely answer to this crossword clue is the 6 letter word PLANCK
I've seen this crossword clue in The Guardian
P
L
A
N
C
K
More clues leading to the result PLANCK
- Speed of light beam's taken in for scientist
- Sounding board for scientist
- He devised a constant sounding board
- Physicist‘s cook disheartened by scheme
- Scientist's scheme hacked midway
- He is known for constant forays into wood
- Physics Nobelist set parameters for one hundred thousand dollars
- German physicist more intelligent than he sounds?
Buddy explains!
The straight part
We know that "He devised a constant" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case he devised a constant = planck.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.