The alternative word for "multiplicity" or "Dissociative Identity Disorder (DID)" is "Multiple Personality Disorder" (MPD). In the past, before the condition was officially recognized as DID, it was commonly referred to as Multiple Personality Disorder. However, the name was changed to Dissociative Identity Disorder in the DSM-IV (Diagnostic and Statistical Manual of Mental Disorders, 4th edition) published in 1994.
The change in terminology was made to better reflect the nature of the condition and to avoid some of the misunderstandings associated with the term "multiple personalities." The term "Dissociative Identity Disorder" emphasizes the role of dissociation in the development of separate identity states, and it is now the widely accepted and clinically recognized term for the condition.