1610s (implied in dissociated) "sever the association or connection of," especially "cut off from society," from Latin dissociatus, past participle of dissociare "to separate from companionship, disunite, set at variance," from dis- "apart" (see dis-) + sociare "to join," from socius "companion, ally," from PIE *sokw-yo-, suffixed form of root *sekw- (1) "to follow."
Attested from 1540s as a past-participle adjective meaning "separated." Dissociated in psychology (1890) was "characterized by mental disjunction," hence dissociated personality (1905) "pathological state in which two or more distinct personalities exist in the same person."
"the severance of association or connection," 1610s, from French dissociation, from Latin dissociationem (nominative dissociatio) "a separation," noun of action from past-participle stem of dissociare (see dissociate).
Proto-Indo-European root meaning "to follow."
It forms all or part of: associate; association; consequence; consequent; dissociate; ensue; execute; extrinsic; intrinsic; obsequious; persecute; persecution; prosecute; pursue; second (adj.) "next after first;" second (n.) "one-sixtieth of a minute;" sect; secundine; segue; sequacious; sequel; sequence; sequester; sociable; social; society; socio-; subsequent; sue; suit; suite; suitor; tocsin.
It is the hypothetical source of/evidence for its existence is provided by: Sanskrit sacate "accompanies, follows;" Avestan hacaiti, Greek hepesthai "to follow;" Latin sequi "to follow, come after," secundus "second, the following;" Lithuanian seku, sekti "to follow;" Old Irish sechim "I follow."