noun
grandson
Rare term; the usual word for 'grandson' is simply 孫 (まご). This compound explicitly specifies a male grandchild.
「孫息子」という言い方はあまり使われず、普通は「孫」で十分です。
The expression 孫息子 is rarely used; normally 孫 is sufficient.
The female counterpart, also rare; explicitly means 'granddaughter'.
Compound of 孫 (まご, 'grandchild') and 息子 (むすこ, 'son'). The exact historical derivation is uncertain, but it follows a pattern of specifying gender in kinship terms.