in (or out of) one's element

noun

1. any of the four substances (earth, air, fire, and water) formerly believed to constitute all physical matter
2. any of these four substances thought of as the natural environment of a class of living beings
3. the natural or suitable environment, situation, etc. for a person or thing
   often in the phrase in (or out of) one's element
4. 1. a component part or quality, often one that is basic or essential: a good story has an element of suspense
   2. a constituent group of a specified kind: the criminal element in a city
   3. a determining factor
   4. any of the data needed or used to make certain calculations, solve a particular problem, etc.
5. on certain electric typewriters, a hollow, metal ball with raised letters, symbols, etc. that print as the corresponding keys are depressed
6. Chem. any substance that cannot be separated into different substances by ordinary chemical methods: all matter is composed of such substances: elements can be transformed into other elements by radioactive decay or by nuclear reactions
7. Comput. one item of data, as in an array (sense )
8. Eccles. the bread and wine of Communion
9. Elec.
   1. any device with terminals at which it can be connected with other electrical devices
   2. the wire coil that becomes glowing hot, as in an electric oven
10. Math.
    1. an infinitesimal part of any magnitude; differential
    2. the point, line, etc. that generates a line, surface, etc.
    3. a part of a set or configuration, as a side of a triangle or a number in a matrix
11. Mil. a subdivision of a unit or formation