Not nearly enough information.
Please post a new question with the coin's date and denomination. Also include any wording EXCEPT "Republique Francaise" or "Liberte, Egalite, Fraternite" - that will be on all French coins and doesn't help narrow down what it is.
it is "sou". It the name of an ancient coin, still used in proverbs ("un sou est un sou" = even a small coin is money - "les sous ne poussent pas sur les arbres" = money does not grow on trees) and in everyday spoken language ("il a des sous" = he is rich)
ecu
it could also be sou. (thats what it is in the crossword i did this morning). i just checked to make sure
Un sou is the French coin with 3 letters. Sou is slang for a small coin of little value.
sou, ecu
écu
the Sou (alternate spelling 'sol') was an old French coin.
'un sou' (alternative spelling 'sol') was a small French coin in the past. That still lives in the language in the expression 'avoir des sous' (to be rich).
FRANC
The old French coin starting with the letter "E" is called the Écu. It was a silver coin used in France from the 13th to the 18th century.
In French, 'huguenot' was the name for protestants. There is no old French coin known as a 'huguenot' - but there is a 1924 US half-dollar called 'Hugenot-Walloon tercentenary'. (follow link)
A franc
Old French coins would be called Francs. now the currency of money there is called Eros, but very old French coins were called Francs. Singular is Franc. Plural is Francs.
"monnaie ancienne"
It is an old French coin, from the 1940 to 1944 era.
The French currency in the 18th century was the franc. Some coins were named by old names like the Louis (the largest coin).
ecu
It must be un sou (or Sol) still used in french language to designate little money. des sous (money) ça vaut pas un sou - it is worth nothing