organogen

from The Century Dictionary.

• noun A chemical element, usually carbon, and, in a less degree, hydrogen, oxygen, nitrogen, sulphur, and phosphorus, which is regarded as the characteristic constituent of an organic compound.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Chem.) A name given to any one of the four elements, carbon, hydrogen, oxygen, and nitrogen, which are especially characteristic ingredients of organic compounds; also, by extension, to other elements sometimes found in the same connection; as sulphur, phosphorus, etc.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun chemistry, dated Any of the four elements — carbon, hydrogen, oxygen, and nitrogen — that are especially characteristic of organic compounds.
• noun chemistry, dated Any of certain other elements sometimes found in organic compounds, such as sulphur and phosphorus.