Crossword Genius

Even when wet, it can burn (4)

Ross

I believe the answer is:

acid

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'can burn' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Maybe there's an association between them I don't understand?

I don't understand the remainder of the clue.

Can you help me to learn more?

(Other definitions for acid that I've seen before include "Drug LSD (colloq.)" , "It is neutralised by alkali" , "Sour - vitriolic" , "See 4 Across" , "Sour, sharp-tasting" .)

I've seen this clue in the Evening Standard.
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