1A person who teaches knowledge or skills, such as at a school or dojo — a teacher or instructor.
私の中学校の先生はとても優しかった。
My middle school teacher was very kind.
水泳の先生に泳ぎ方を教わっている。
I'm learning how to swim from a swimming instructor.
先生の説明はいつも分かりやすい。
The teacher's explanations are always easy to understand.
あの先生は生徒一人ひとりに丁寧に対応する。
That teacher deals with each student carefully and attentively.
2An honorific title used to address professionals such as teachers, doctors, or lawyers, or other respected figures — often attached after a name as "~sensei."
田中先生、少しお時間よろしいですか。
Dr./Professor Tanaka, do you have a moment?
弁護士の先生に相談してから決めます。
I'll decide after consulting with the lawyer.
かかりつけの先生に薬を出してもらった。
My regular doctor prescribed me some medicine.
3A joking or affectionate way of calling a close friend "sensei," sometimes with a hint of teasing.
スマホに詳しい友達を、みんな「先生」と呼んでいる。
Everyone jokingly calls the friend who's good with smartphones "sensei."
「さすが先生、詳しいですね」と冗談で言われた。
I was jokingly told, "As expected of the master, you really know your stuff."
4An archaic meaning referring to an elder or someone born earlier; rarely used in this sense in modern Japanese.