...is for Merde.
The ultimate French swear word. It translates as "Shit", but doesn't seem as vulgar or socially unacceptable. It can also be used simply for emphasis, in a fairly untranslatable manner, for example:
"Bien sûr que j'ai fait ma déclaration d'impôts, merde !" - "Of course I've done my tax returns, merde!". Obviously, you could use "fucking well" here, with the same function ("Of course I've fucking well done my tax forms!"), but it's not the same and is definitely a lot more vulgar.
Merde is a much softer swear word, and I love it!