phen(o)-

Also phenoxy‑.

Benzene compounds; showing.

Greek phaino‑, shining; phainein, to show.

The link between these senses is that the first benzene compounds were obtained from coal tar, a by-product of the production of illuminating gas.

The key chemical name is phenol (adjective phenyl), obtained from coal tar and used in chemical manufacture. Other examples are phenobarbitone, a narcotic and sedative barbiturate drug used chiefly to treat epilepsy, and phenanthrene, a crystalline hydrocarbon present in coal tar.

The compound prefix phenoxy‑ (see ox(y)‑²) indicates the presence of the radical C₆H₅O—, as in phenoxyacetic acid, one of a group that includes the weedkillers 2,4–D and MCPA, and phenoxybenzamine, a drug that dilates blood vessels in the treatment of conditions involving poor circulation.

The sense of ‘showing’ appears in phenomenon, and also in phenotype, the set of observable characteristics of an organism resulting from the interaction of its genotype with the environment, and phenocryst (Greek krustallos, crystal), a large or conspicuous crystal in a porphyritic rock.