senior pupil; senior disciple; senior student
Refers to a more experienced student under the same teacher or master, often in traditional arts, martial arts, or apprenticeship contexts. Contrasts with 弟弟子 (おとうとでし, junior pupil).
See also: 弟弟子
He is my senior disciple, having become a pupil of the same master ten years before me.
As a senior student, I am responsible for guiding the juniors.
Compound of 兄 (あに, older brother) and 弟子 (でし, disciple/pupil). The reading あにでし follows standard rendaku for 弟子 in this context.