Monsieur altered canton to include limits of Basel and an Alp (4,5)
I believe the answer is:
mont blanc
'an alp' is the definition.
The answer and definition can be both natural objects as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'monsieur altered canton to include limits of basel' is the wordplay.
'monsieur' becomes 'm' ().
'altered' indicates an anagram.
'to include' means one lot of letters goes inside another.
'limits of' suggests removing the centre.
'basel' with its middle taken out is 'bl'.
'canton' with letters rearranged gives 'ontanc'.
'ontanc' going around 'bl' is 'ontblanc'.
'm'+'ontblanc'='MONT BLANC'
'and' acts as a link.
Can you help me to learn more?
(Other definitions for mont blanc that I've seen before include "Highest Alpine peak" , "High spot in France (and partly 18)" , "Highest peak in the Alps" , "peak of continental Europe" , "Fancy pen" .)