Haecceity
Haecceity (transliterated from the Latin haecceitas) is a term from medieval philosophy first coined by Duns Scotus which denotes the discrete qualities, properties or characteristics of a thing which make it a particular thing. Haecceity is a person or object’s “thisness”.
[…]

Haecceity and Quiddity
Haecceity may be defined in some dictionaries as simply the “essence” of a thing, or as a simple synonym for quiddity or hypokeimenon. However, such a definition deprives the term of its subtle distinctiveness and utility. Whereas haecceity refers to aspects of a thing which make it a particular thing, quiddity refers to the universal qualities of a thing, its “whatness”, or the aspects of a thing which it may share with other things and by which it may form part of a genus of things. […]

It is important to note that while terms such as haecceity, quiddity, noumenon and hypokeimenon all evoke the essence of a thing, they each have subtle differences and refer to different aspects of the thing’s essence.