To complain so may be common all over the world (12)
I believe the answer is:
cosmopolitan
'common all over the world' is the definition.
I can't tell whether this definition defines the answer.
'to complain so may be' is the wordplay.
'may be' indicates anagramming the letters.
'to'+'complain'+'so'='tocomplainso'
'tocomplainso' anagrammed gives 'COSMOPOLITAN'.
Can you help me to learn more?
(Other definitions for cosmopolitan that I've seen before include "international" , "all around the world" , "Familiar with different cities and cultures" , "Familiar with many cultures" , "cocktail for a > man of the world" .)