The noun of ‘dissever’, to divide or sever something from something else. Also ‘disseverance’.  Used here in reference to a severely split personality.
‘For it is probable that when people talk aloud, the selves (of which there may be more than two thousand) are conscious of disseverment, and are trying to communicate, but when communication is established they fall silent.’
Source: Virginia Woolf, Orlando, ed. Rachel Bowlby, Oxford: World’s Classics, 1992, p. 299-300
