Even when wet, it can burn (4)
I believe the answer is:
acid
'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" .)