The eldest child in a family — the first-born child (can be a son or daughter).
長子として家業を継ぐ期待がかかっている。
There are expectations that, as the eldest child, he will inherit the family business.
彼女は三人兄弟の長子だ。
She is the eldest of three siblings.
長子には責任感が求められることが多い。
Eldest children are often expected to have a sense of responsibility.
Used to refer specifically to the eldest son — the first-born male child (an older/older-fashioned usage).
家督は長子が継ぐという考え方があった時代もある。
There was a time when the headship of the household was inherited by the eldest son.
古い記録では『長子』が家を相続すると書かれている。
Old records state that the eldest son would inherit the household.