Yes I remember now thinking that the term "essentialism" probably applies more to Aristotle and "ideal forms" more to Plato. The concept appears almost the same with the main issue being "where" this metaphysical entity exists.
I suppose for the sake of exercise it would be good to try to state concisely what is Epicurus' answer to essentialism. No doubt the answer involves the way atoms move through void, but that's probably not complete without combining it with how those atoms interact with our senses, anticipations, and feelings. Without the full picture (and here I'm thinking about how Lucretius says that it's not by the rays of light themselves that we understand anything) I don't think we have a full picture of what it means to be "real" to us as humans.