Haecceity hæk-see-ê-tee… 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”.
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 & by which it may form part of a genus of things.
Haecceity & quiddity have been subsumed under the term, “essentialism” which Richard Dawkins has called “the dead hand of Plato”