Spirit

Aether (or ether, also known as quintessence, although that's just another word for 'fifth element'). One of my friends had a ouija board experience in which the alleged spirit claimed it inhabited either - which was traditionally held to be what the non-terrestrial universe was made of.

There's more about it here:

http://en.wikipedia.org/wiki/Aether_%28classical_element%29

Depending on what religion as the greeks believed in Aether, Latin in quintessence and Neo Paganism in lightening/spirit.

http://en.wikipedia.org/wiki/Classical_element

The Greek Classical Elements (Earth, Water, Air, Fire, and Idea) date from pre-Socratic times and persisted throughout the Middle Ages and into the Renaissance,

http://en.wikipedia.org/wiki/Classical_elements

Same as it is for many of us now... spirit. Imagine a celtic cross. Earth, air, fire and water are represented by the arms of the cross, whilst sprit is represented by the centre of the cross. Christians aren't the only ones who use a cross for visualisation/representation.