functional group
Chemistry term for a specific group of atoms within a molecule that is responsible for the characteristic chemical reactions of that molecule.
The functional group of an alcohol is the hydroxy group.
This molecule contains a functional group called a carboxyl group.
Compound of 官能 (function, from 官 'official' + 能 'ability') and 基 (base, group). A modern chemistry term, likely a calque from English 'functional group'.