The most common and most likely answer to this crossword clue is the 8 letter word VANADIUM
I've seen this crossword clue in The Times
V
A
N
A
D
I
U
M
Buddy explains!

The straight part
We know that "Metal" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case metal = vanadium.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 VANADIUM mean?
VANADIUM noun- A chemical element (symbol V) with atomic number 23; it is a transition metal, used in the production of special steels.
- A single atom of this element.