secondary carbon atom
Technical term in organic chemistry: a carbon atom bonded to two other carbon atoms.
A secondary carbon atom is bonded to two other carbon atoms.
Primary carbon atom: bonded to only one other carbon atom.
Tertiary carbon atom: bonded to three other carbon atoms.
Compound of 第二級 (secondary, second class) + 炭素 (carbon) + 原子 (atom). A direct calque from English 'secondary carbon atom'.