Mammoth Uncensored Word List:
28 - 19 letter words starting with n

neurofibromatosises neuropharmacologies neuropharmacologist nonadministratively nonagintacentillion nonarteriosclerotic noncorticosteroidal noncrystallographic nondisqualification nonenantioselective nonenforceabilities nonextraterrestrial nongastrointestinal nonintentionalistic noninterventionists nonproductivenesses nonrelativistically nonrepresentational nonreproductiveness nonrespectabilities nonresponsibilities nonsubconsciousness nonsubstitutionally nontraditionalistic nontransmissibility nontransportability novemvigintillionth noventrigintillions