Mammoth Uncensored Word List:
22 - 17 letter words starting with se

semiautomatically semiconsciousness semidocumentaries semidomestication semiobjectiveness semiobliviousness semipornographies semiprofessionals sententiousnesses septendecilliards septendecillionth septingentillions septuagintilliard septuagintillions serviceablenesses sesquicentenaries sesquicentennials sesquipedalophobe sestrigintillions sesvigintillionth sexagintilliardth sexagintillionths