A question Descartes implicitly asked his pal (3)
I believe the answer is:
ami
'descartes implicitly asked his pal' is the definition.
The definition suggests a singular noun which matches the answer.
'a question' is the wordplay.
'question' becomes 'mi' (I can't explain this - if you can you should give a lot more credence to this answer).
'a'+'mi'='AMI'
Can you help me to learn more?
(Other definitions for ami that I've seen before include "Friend (Fr.)" , "Mon . . . - my French friend" , "buddy" , "friend abroad?" , "Parisian's friend" .)