Should not the "personality" have been pluralized in "Multiple Personality Disorder"?
Is the single usage of "personality" with prepending "multiple" a professional jargon or it is the correct English usage?
Should not the "personality" have been pluralized in "Multiple Personality Disorder"?
Is the single usage of "personality" with prepending "multiple" a professional jargon or it is the correct English usage?
In compound adjectives of this kind, where the first element is a number (or, as in this case, a numeric adjective), the second element is indeed always in singular form. Examples include three-dog night (a night so cold that you have to curl up with three dogs for warmth), Six-Party Talks (about North Korea, a few years back), seven-layer cake, and so forth.
Also see "toothbrush," "orange grove," and "tool box." As Alex says above, compound constructions generally agree in number, such that if one item is singular (brush, grove, box), the other will agree with it even though referring to multiple items.