Cryptic crossword clue
Bizarre idea about cold metal being radioactive element 8

The most common and most likely answer to this crossword clue is the 8 letter word ACTINIDE

I've seen this crossword clue in The Daily Telegraph
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Buddy explains!

The straight part
We know that "radioactive element" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case radioactive element = actinide.
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 ACTINIDE mean?

ACTINIDE noun
  1. Any of the 14 radioactive elements of the periodic table that are positioned under the lanthanides, to which they have similar chemistry.

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