2. An artifact that is one of the individual parts of which a composite entity is made up; especially a part that can be separated from or attached to a system Noun
3. Any of the more than 100 known substances (of which 92 occur naturally) that cannot be separated into simpler substances and that singly or in combination constitute all matter Noun
4. The most favorable environment for a plant or animal Noun
5. One of four substances thought in ancient and medieval cosmology to constitute the physical universe Noun
6. The situation in which you are happiest and most effective Noun
7. A straight line that generates a cylinder or cone Noun