Message in taxi taken by the French (5)
I believe the answer is:
cable
'message' is the definition.
(as in sending a cable to someone)
'taxi taken by the french' is the wordplay.
'taxi' becomes 'cab' (synonyms).
'taken by' means one lot of letters go next to another.
'the french' becomes 'le' ('the' in French).
'cab'+'le'='CABLE'
'in' acts as a link.
(Other definitions for cable that I've seen before include "Conductor for transmitting electric power" , "Wire; message" , "Communications wire" , "Naut. length; transmit" , "Telegram; thick rope" .)