French mathematician swapping units of temperature with messenger (7)
I believe the answer is:
courier
'messenger' is the definition.
(I know that messenger can be written as courier)
'french mathematician swapping units of temperature' is the wordplay.
I cannot quite see how this works, but
'of' could be 'o' and 'o' is located in the answer.
'temperature' could be 'curie' (Curie temperature is an example) and 'curie' is found in the leftover letters.
A single letter 'r' remains which might be clued in a way I don't see.
This explanation may well be incorrect...
'with' is the link.
Can you help me to learn more?
(Other definitions for courier that I've seen before include "Dispatch rider" , "Travel guide" , "Messenger conveying news or document (7)" , "Diplomatic messenger" , "Messenger, runner" .)