The most common and most likely answer to this crossword clue is the 8 letter word CADUCEUS
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The straight part
We know that "impaling rod" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case impaling rod = caduceus.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 CADUCEUS mean?
CADUCEUS noun- The official wand carried by a herald in ancient Greece and Rome, specifically the one carried in mythology by Hermes, the messenger of the gods, usually represented with two snakes twined around it.
- A symbol (☤) representing a staff with two snakes wrapped around it, used to indicate merchants and messengers. It is also sometimes incorrectly used as a symbol of medicine.