Don't be surprised if, when struck, it flares up! (5)
I believe the answer is:
vesta
'don't' is the definition.
Both the answer and definition are singular nouns.
Perhaps there's an association between them I don't understand?
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for vesta that I've seen before include "heavenly body" , "Stave (anag.)" , "Roman goddess of the hearth" , "Asteroid; goddess; match" , "Roman goddess; match" .)