General meaning (fundamental nature):
* Quidditas (formal, philosophical)
* Core
* Heart
* Spirit
* Nature
* Substance
* Intrinsic
* Inherent
* Fundamental
Meaning related to fragrance or flavor:
* Aroma
* Scent
* Flavor
* Bouquet (for wine)
Meaning related to a distilled or concentrated form:
* Extract
* Concentrate
* Quintessence
* Elixir
Meaning related to the soul or spirit:
* Soul
* Spirit
* Being
* Life force
To choose the most appropriate synonym, consider the specific context and the meaning you want to convey.