The most common and most likely answer to this crossword clue is the 9 letter word BERYLLIUM
I've seen this crossword clue in The Guardian
B
E
R
Y
L
L
I
U
M
More clues leading to the result BERYLLIUM
Buddy explains!

The straight part
We know that "Be" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case be = beryllium.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 BERYLLIUM mean?
BERYLLIUM noun- The chemical element (symbol Be) with an atomic number of 4; a soft silvery-white low density alkaline earth metal with specialist industrial applications.
- An atom of this element.