Mammoth Uncensored Word List:
21 - 15 letter words starting with fr

fractionalising fractionalizing fractionisation fractionization fractiousnesses fragmentariness frangiblenesses fraternisations fraternizations freeheartedness frenchification frenuloplasties frightfulnesses frivolousnesses frontoethmoidal frontomaxillary frontooccipital frontozygomatic fructifications fructuousnesses fruitlessnesses