Big league of countries, initially — with common interests (4)
I believe the answer is:
bloc
'with common interests' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
'big league of countries initially' is the wordplay.
'initially' indicates taking the first letters.
The first letters of 'big league of countries' is 'BLOC'.
Can you help me to learn more?
(Other definitions for bloc that I've seen before include "Political coalition" , "Group with a common policy" , "Group whose members have common objectives" , "Combination of nations" , "Group of allied nations" .)