Note, explosive danger surrounds it (7)
I believe the answer is:
grenade
'note' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'explosive danger surrounds it' is the wordplay.
'explosive' indicates anagramming the letters.
'surrounds' means one lot of letters goes inside another.
'it' becomes 'e' ('e' can mean 'electronic' which is similar to 'IT').
'danger' is an anagram of 'grnade'.
'grnade' placed around 'e' is 'GRENADE'.
Can you help me to learn more?
(Other definitions for grenade that I've seen before include "Bomb with a pin" , "Angered (anag)" , "Small bomb thrown by hand" , "Hand-thrown bomb" , "Hand-thrown explosive" .)