Earth, air, fire, or water," from Old French element (10c.), from Latin elementem "rudiment, first principle, matter in its most basic form".
Meaning "simplest component of a complex substance"
A fundamental, essential, or irreducible constituent of a composite entity.
A substance that cannot be broken down into simpler substances by chemical means. 115 distinct elements are classified in the Periodic Table.
A natural habitat, sphere of activity, environment, etc.:
to be in one's element; Water is the element of fish.
I am in my element. Meaning: I am in a place or doing something that feels most comfortable to me. This place or activity suits me very well.
Source: http://www.dictionary.com/browse/element (derived, 23-3-2016)