noun
Refers specifically to the third-born son in a family. Often used in family registers, introductions, or when distinguishing birth order.
彼は三男で、上に兄が二人います。
He is the third son, with two older brothers above him.
noun
three sons
Used when counting or referring to a group of three male children. Less common than the 'third son' sense, and context usually makes the meaning clear.
彼には三男一女の子供がいる。
He has three sons and one daughter.