Azo

Describing chemical compounds containing an azo group (N=N), a double bond between two nitrogen atoms, commonly found in dyes and pigments.

From German 'Azofarbstoffe' (azo dyes), itself from 'azo-' possibly meaning 'without oxygen' or from 'azoic' (pertaining to life). Entered English in the 1870s as synthetic dye chemistry exploded.