A French cycling siesta is least relaxing (9)
I believe the answer is:
uneasiest
'least relaxing' is the definition.
I can't tell whether this defines the answer.
'a french cycling siesta' is the wordplay.
'a french' becomes 'une' ('a' in French).
'cycling' indicates anagramming the letters.
'siesta' is an anagram of 'asiest'.
'une'+'asiest'='UNEASIEST'
'is' acts as a link.
Can you help me to learn more?
(Other definitions for uneasiest that I've seen before include "Most anxious" , "Most like a crowned head" , "very hard?" , "extremely nervous" .)