noun
A somewhat familiar or affectionate term for the third-born son in a family. Often used in contrast with 長男 (eldest son) and 次男 (second son). The suffix 坊 adds a casual, boyish nuance.
See also: 次男坊
うちの三男坊はまだ小学生です。
Our third son is still in elementary school.
三男坊が生まれて、家族は五人になった。
With the birth of our third son, our family became five.
長男 is the formal term for 'eldest son', without the casual 坊 suffix.
次男 is the formal term for 'second son', without the casual 坊 suffix.
三男 is the neutral, formal term for 'third son'. 三男坊 is more colloquial and affectionate.
Compound of 三 (san, 'three'), 男 (nan, 'male'), and 坊 (bō, 'boy' or 'son'), a suffix often used in familiar terms for sons.