Word riddle

The Walloons are a French-speaking people from Belgium.

The word, 'Walloon' contains two consecutive double letters, a double 'L' followed by a double 'O'.

There is only one word in English that contains three consecutive double letters. It is not an uncommon word.

Do you know what it is?


[posed to me by chib, there are at least two possible answers but the root is the same]