Mammoth Uncensored Word List:
99 - 13 letter words starting with so

sociabilities socialisation socialization sociocentrism sociocultural socioeconomic sociolinguist sociologistic sociometrists sodomitically softheartedly solarisations solarizations solderability soldierliness solemnisation solemnization solicitations solicitorship solidungulate solidungulous solifidianism solifluctions soliloquisers soliloquising soliloquizers soliloquizing solonisations solonizations solublenesses solvabilities somaesthesias somatological somatologists somatoplastic somatopleural somatopleures somatopleuric somatosensory somatostatins somatotrophic somatotrophin somatotropins somersaulting somesthesises somnambulance somnambulants somnambulated somnambulates somnambulator somnambulisms somnambulists somnifacients somniferously somniloquence somniloquised somniloquises somniloquisms somniloquists somniloquized somniloquizes somnipathists somnolescence songfulnesses sonneteerings soothfastness sophistically sophisticated sophisticates sophisticator soporifically sorbabilities sorbefacients sorbitisation sorbitization sorosilicates sorrowfulness soteriologies sottishnesses soulfulnesses soulsearching soundlessness soundproofers soundproofing soundtracking sousaphonists southeasterly southeastward southerliness southernising southernizing southernwoods southwesterly southwestward sovereignties sovereigntist sovietisation sovietization sovietologist