A concern as it spread across the pond (12)
I believe the answer is:
transoceanic
'across the pond' is the definition.
I can't tell whether this defines the answer.
'a concern as it spread' is the wordplay.
'spread' is an anagram indicator.
'a'+'concern'+'as'+'it'='aconcernasit'
'aconcernasit' is an anagram of 'TRANSOCEANIC'.
Can you help me to learn more?
(Other definitions for transoceanic that I've seen before include "Crossing, eg, the Atlantic" , "across the water" , "across the Pacific, say?" .)