Take heed of national uprising to put end to injustice (4)
I believe the answer is:
note
'take heed of' is the definition.
(I've seen this in another clue)
'national uprising to put end to injustice' is the wordplay.
'national' becomes 'n' (abbreviation listed in Chambers).
'uprising' shows that the letters should be reversed in order.
'put' says to put letters next to each other.
'end to' says to take the final letters.
The last letter of 'injustice' is 'e'.
'to' reversed gives 'ot'.
'n'+'ot'+'e'='NOTE'
(Other definitions for note that I've seen before include "mention" , "Fiver, say" , "A piece of paper money" , "Detect and remember" , "Record - piece of music" .)