Not a new acronym (4)
I believe the answer is:
nato
'acronym' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how one could define the other.
'not a new' is the wordplay.
'new' indicates an anagram.
'not'+'a'='nota'
'nota' with letters rearranged gives 'NATO'.
Can you help me to learn more?
(Other definitions for nato that I've seen before include "N. Atlantic alliance" , "International organisation for collective security" , "Western mil. alliance" , "Military bloc" , "Military alliance (acronym)" .)