I roughly knew the meaning of the word because I had heard it being used rather often. Today, I hit something interesting when I decided to look it up in dictionary.com.
Quintessential element is the fifth essential (quint for five) element of universe, which is ether. The other four are air, earth, water and fire.
What surprises me is the fact that the same set of objects are quoted in Indian text as the panchbhoota, or the five elements. It's not a trivial co-incidence again, if at all a co-incidence.
Anyone has any idea regarding the origins of this idea of elements in both latin and sanskrit scriptures?