Exchange rate halved and quadrupled around mid-May (4-1-4)
I believe the answer is:
tete-a-tete
'exchange' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps you can see a link between them that I can't see?
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for tete-a-tete that I've seen before include "Private meeting" , "Private conversation between two French people" , "Private conversation between two people as in France" , "Private couple's conversation" , "Informal chat" .)