Expedition to the French metropolis goes round river (8)
I believe the answer is:
alacrity
'expedition' is the definition.
(I've seen this before)
'to the french metropolis goes round river' is the wordplay.
'to the french' becomes 'ala'.
'metropolis' becomes 'city' ('city' can be a synonym of 'metropolis'**).
'goes round' means one lot of letters goes inside another.
'river' becomes 'r'.
'city' going around 'r' is 'crity'.
'ala'+'crity'='ALACRITY'
(Other definitions for alacrity that I've seen before include "'Quick, cheerful enthusiasm (8)'" , "Prompt enthusiasm" , "Expedition" , "Enthusiasm; speed" , "Briskness, liveliness" .)