Mammoth Uncensored Word List:
22 - 13 letter words starting with ru

rubberneckers rubbernecking rubberstamped rubicundities rudimentarily ruggedisation ruggedization ruinousnesses rumbledethump rumbustiously rumelgumption rumlegumption rumormongered ruralisations ruralizations russomaniacal russophilists russophobiacs russophobists rutherfordium ruthfulnesses ruttishnesses