Mammoth Uncensored Word List:
24 - 15 letter words starting with as

asclepiadaceous assentivenesses assertivenesses assiduousnesses assignabilities assimilationism assimilationist associabilities associationisms associationists associativities astrobiological astrobiologists astrochemically astrodynamicist astrogeologists astronautically astronavigation astronavigators astrophotograph astrophotometer astrophotometry astrophysically astrophysicists