Full Idea
Essentialism says some individuals have certain 'interesting' necessary properties. If it exists, it has that property. The properties are 'interesting' as had in virtue of their own peculiar natures, rather than as general necessary truths.
Gist of Idea
Essences are the interesting necessary properties resulting from a thing's own peculiar nature
Source
Alan McMichael (The Epistemology of Essentialist Claims [1986], Intro)
Book Reference
'Midwest Studs XI:Essentialism', ed/tr. French,Uehling,Wettstein [Minnesota 1986], p.33
A Reaction
[compressed] This is a modern commentator caught between two views. The idea that essence is the non-trivial-necessary properties is standard, but adding their 'peculiar natures' connects him to Aristotle, and Kit Fine's later papers. Good!