Full Idea
To make any nominal essence, it is necessary that the ideas whereof it consists have such an union as to make but one idea, how compounded soever.
Gist of Idea
To be a nominal essence, a complex idea must exhibit unity
Source
John Locke (Essay Conc Human Understanding (2nd Ed) [1694], 3.06.28)
Book Reference
Locke,John: 'Essay Concerning Human Understanding', ed/tr. Nidditch,P.H. [OUP 1979], p.455
A Reaction
This distinguishes nominal essences from his other 'mixed modes', which are just collocations of ideas, but not necessarily exhibiting unity.