The most common and most likely answer to this crossword clue is the 7 letter word RHENIUM
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More clues leading to the result RHENIUM
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The cryptic/wordplay part
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What does RHENIUM mean?
RHENIUM noun- A metallic chemical element (symbol Re) with an atomic number of 75: a heavy, silvery-gray transition metal.
- A single atom of this element.