noun
former teacher; deceased teacher
Refers to a teacher one previously studied under, often with respect. May imply the teacher has passed away, but context determines this.
先師の教えを今でも大切にしている。
I still cherish the teachings of my former teacher.
先師の命日に墓参りに行った。
I visited the grave on the anniversary of my late teacher's death.
Compound of 先 (previous, former) and 師 (teacher, master). The reading せんし follows standard on'yomi.