The most common and most likely answer to this crossword clue is the 8 letter word OXIDISED
I've seen this crossword clue in Financial Times
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More clues leading to the result OXIDISED
Buddy explains!
The straight part
We know that "Having undergone chemical change" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case having undergone chemical change = oxidised.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 OXIDISED mean?
OXIDISED verb- To combine with oxygen or otherwise make an oxide.
- To increase the valence (or the positive charge) of an element by removing electrons.
- To coat something with an oxide.
- To become oxidized.
- That has reacted with oxygen, or been modified by oxidation