This strange sum recalled Panama, perhaps (7)
I believe the answer is:
isthmus
'this strange sum recalled panama perhaps' is the definition.
The definition suggests a singular noun which matches the answer.
'this strange sum recalled' is the wordplay.
'strange' indicates anagramming the letters.
'recalled' shows that the letters should be reversed in order.
'sum' in reverse letter order is 'mus'.
'this' anagrammed gives 'isth'.
'isth'+'mus'='ISTHMUS'
Can you help me to learn more?
(Other definitions for isthmus that I've seen before include "Narrow strip of land joining two larger entities" , "Neck of land connecting larger areas" , "Narrow strip joining larger areas of land" , "Narrow neck of land connecting two larger portions" , "Narrow strip linking two larger areas of land" .)